Improve documentation of memory_cleanse()

So far, the documentation of memory_cleanse() is a verbatim copy of
the commit message in BoringSSL, where this code was originally
written. However, our code evolved since then, and the commit message
is not particularly helpful in the code but is rather of historical
interested in BoringSSL only.

This commit improves improves the comments around memory_cleanse()
and gives a better rationale for the method that we use. This commit
touches only comments.

0 files changed, 0 insertions, 0 deletions