[REG 6.4] syncqt.cpp does not install headers marked with qt_deprecates pragma

According to https://codereview.qt-project.org/c/qt/qtbase/+/415613
headers that were previously listed in sync.profile's deprecatedheaders dictionary, are now handled by adding a #pragma qt_deprecates(name) in a header file.

These deprecated forwarding header files are created in the build directory, but they do not end up installed.