Merge #16707: qt: Remove obsolete QModelIndex::child()

c53667764ea65c0f8661358759b0124f808ce587 qt: Remove obsolete QModelIndex::child() (Hennadii Stepanov)

Pull request description:

  The `QModelIndex::child()` member function is [obsolete](https://doc.qt.io/qt-5.12/qmodelindex-obsolete.html) since Qt 5.12.

  This PR removes it, does not change behavior and keeps compatibility with [Qt 5.5.1](https://github.com/bitcoin/bitcoin/pull/15393).

  Here is an excerpt from the master build log:
  ```
  qt/receivecoinsdialog.cpp: In member function ‘void ReceiveCoinsDialog::copyColumnToClipboard(int)’:
  qt/receivecoinsdialog.cpp:264:111: warning: ‘QModelIndex QModelIndex::child(int, int) const’ is deprecated: Use QAbstractItemModel::index [-Wdeprecated-declarations]
       GUIUtil::setClipboard(model->getRecentRequestsTableModel()->data(firstIndex.child(firstIndex.row(), column), Qt::EditRole).toString());
                                                                                                                 ^
  In file included from /home/hebasto/Qt/5.13.0/gcc_64/include/QtWidgets/qabstractitemview.h:45:0,
                   from /home/hebasto/Qt/5.13.0/gcc_64/include/QtWidgets/qheaderview.h:44,
                   from /home/hebasto/Qt/5.13.0/gcc_64/include/QtWidgets/QHeaderView:1,
                   from ./qt/guiutil.h:12,
                   from ./qt/receivecoinsdialog.h:8,
                   from qt/receivecoinsdialog.cpp:7:
  /home/hebasto/Qt/5.13.0/gcc_64/include/QtCore/qabstractitemmodel.h:457:20: note: declared here
   inline QModelIndex QModelIndex::child(int arow, int acolumn) const
                      ^~~~~~~~~~~
  ```

ACKs for top commit:
  laanwj:
    Code review ACK c53667764ea65c0f8661358759b0124f808ce587
  promag:
    ACK c53667764ea65c0f8661358759b0124f808ce587, just read the change.
  jonasschnelli:
    utACK c53667764ea65c0f8661358759b0124f808ce587

Tree-SHA512: 99fcb6ff60a6d47b925bda9f14006269eaad09ba4f7a41ac4975c6cf04bd906b58aed721cbfa0be7da8e6613d92e30d4be18b7e4d3960f026c7226558a4c3196

0 files changed, 0 insertions, 0 deletions