Remove polylith/API mode (#2967)

This removes most of the code used for polylith/API mode.

This removes the `/api` internal endpoints entirely. 

Binary size change roughly 5%: 
```
51437560 Feb 13 10:15 dendrite-monolith-server # old
48759008 Feb 13 10:15 dendrite-monolith-server # new
```

3 files changed, 0 insertions, 187 deletions

diff --git a/internal/httputil/http.go b/internal/httputil/http.go
deleted file mode 100644
index ad26de51..00000000
--- a/internal/httputil/http.go
+++ /dev/null
@@ -1,93 +0,0 @@
-// Copyright 2020 The Matrix.org Foundation C.I.C.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package httputil
-
-import (
-	"bytes"
-	"context"
-	"encoding/json"
-	"fmt"
-	"io"
-	"net/http"
-	"net/url"
-	"strings"
-
-	"github.com/opentracing/opentracing-go"
-	"github.com/opentracing/opentracing-go/ext"
-)
-
-// PostJSON performs a POST request with JSON on an internal HTTP API.
-// The error will match the errtype if returned from the remote API, or
-// will be a different type if there was a problem reaching the API.
-func PostJSON[reqtype, restype any, errtype error](
-	ctx context.Context, span opentracing.Span, httpClient *http.Client,
-	apiURL string, request *reqtype, response *restype,
-) error {
-	jsonBytes, err := json.Marshal(request)
-	if err != nil {
-		return err
-	}
-
-	parsedAPIURL, err := url.Parse(apiURL)
-	if err != nil {
-		return err
-	}
-
-	parsedAPIURL.Path = InternalPathPrefix + strings.TrimLeft(parsedAPIURL.Path, "/")
-	apiURL = parsedAPIURL.String()
-
-	req, err := http.NewRequest(http.MethodPost, apiURL, bytes.NewReader(jsonBytes))
-	if err != nil {
-		return err
-	}
-
-	// Mark the span as being an RPC client.
-	ext.SpanKindRPCClient.Set(span)
-	carrier := opentracing.HTTPHeadersCarrier(req.Header)
-	tracer := opentracing.GlobalTracer()
-
-	if err = tracer.Inject(span.Context(), opentracing.HTTPHeaders, carrier); err != nil {
-		return err
-	}
-
-	req.Header.Set("Content-Type", "application/json")
-
-	res, err := httpClient.Do(req.WithContext(ctx))
-	if res != nil {
-		defer (func() { err = res.Body.Close() })()
-	}
-	if err != nil {
-		return err
-	}
-	var body []byte
-	body, err = io.ReadAll(res.Body)
-	if err != nil {
-		return err
-	}
-	if res.StatusCode != http.StatusOK {
-		if len(body) == 0 {
-			return fmt.Errorf("HTTP %d from %s (no response body)", res.StatusCode, apiURL)
-		}
-		var reserr errtype
-		if err = json.Unmarshal(body, &reserr); err != nil {
-			return fmt.Errorf("HTTP %d from %s - %w", res.StatusCode, apiURL, err)
-		}
-		return reserr
-	}
-	if err = json.Unmarshal(body, response); err != nil {
-		return fmt.Errorf("json.Unmarshal: %w", err)
-	}
-	return nil
-}
diff --git a/internal/httputil/internalapi.go b/internal/httputil/internalapi.go
deleted file mode 100644
index 22f436e3..00000000
--- a/internal/httputil/internalapi.go
+++ /dev/null
@@ -1,93 +0,0 @@
-// Copyright 2022 The Matrix.org Foundation C.I.C.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package httputil
-
-import (
-	"context"
-	"encoding/json"
-	"fmt"
-	"net/http"
-	"reflect"
-
-	"github.com/matrix-org/util"
-	"github.com/opentracing/opentracing-go"
-)
-
-type InternalAPIError struct {
-	Type    string
-	Message string
-}
-
-func (e InternalAPIError) Error() string {
-	return fmt.Sprintf("internal API returned %q error: %s", e.Type, e.Message)
-}
-
-func MakeInternalRPCAPI[reqtype, restype any](metricsName string, enableMetrics bool, f func(context.Context, *reqtype, *restype) error) http.Handler {
-	return MakeInternalAPI(metricsName, enableMetrics, func(req *http.Request) util.JSONResponse {
-		var request reqtype
-		var response restype
-		if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
-			return util.MessageResponse(http.StatusBadRequest, err.Error())
-		}
-		if err := f(req.Context(), &request, &response); err != nil {
-			return util.JSONResponse{
-				Code: http.StatusInternalServerError,
-				JSON: &InternalAPIError{
-					Type:    reflect.TypeOf(err).String(),
-					Message: fmt.Sprintf("%s", err),
-				},
-			}
-		}
-		return util.JSONResponse{
-			Code: http.StatusOK,
-			JSON: &response,
-		}
-	})
-}
-
-func MakeInternalProxyAPI[reqtype, restype any](metricsName string, enableMetrics bool, f func(context.Context, *reqtype) (*restype, error)) http.Handler {
-	return MakeInternalAPI(metricsName, enableMetrics, func(req *http.Request) util.JSONResponse {
-		var request reqtype
-		if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
-			return util.MessageResponse(http.StatusBadRequest, err.Error())
-		}
-		response, err := f(req.Context(), &request)
-		if err != nil {
-			return util.JSONResponse{
-				Code: http.StatusInternalServerError,
-				JSON: err,
-			}
-		}
-		return util.JSONResponse{
-			Code: http.StatusOK,
-			JSON: response,
-		}
-	})
-}
-
-func CallInternalRPCAPI[reqtype, restype any](name, url string, client *http.Client, ctx context.Context, request *reqtype, response *restype) error {
-	span, ctx := opentracing.StartSpanFromContext(ctx, name)
-	defer span.Finish()
-
-	return PostJSON[reqtype, restype, InternalAPIError](ctx, span, client, url, request, response)
-}
-
-func CallInternalProxyAPI[reqtype, restype any, errtype error](name, url string, client *http.Client, ctx context.Context, request *reqtype) (restype, error) {
-	span, ctx := opentracing.StartSpanFromContext(ctx, name)
-	defer span.Finish()
-
-	var response restype
-	return response, PostJSON[reqtype, restype, errtype](ctx, span, client, url, request, &response)
-}
diff --git a/internal/httputil/paths.go b/internal/httputil/paths.go
index 62eff041..d0687542 100644
--- a/internal/httputil/paths.go
+++ b/internal/httputil/paths.go
@@ -21,7 +21,6 @@ const (
 	PublicMediaPathPrefix      = "/_matrix/media/"
 	PublicStaticPath           = "/_matrix/static/"
 	PublicWellKnownPrefix      = "/.well-known/matrix/"
-	InternalPathPrefix         = "/api/"
 	DendriteAdminPathPrefix    = "/_dendrite/"
 	SynapseAdminPathPrefix     = "/_synapse/"
 )