Remove the remaining traces of QT3_SUPPORT

Remove the remaining traces of QT3_SUPPORT

The only place that now still knows about it is moc,
so it can still parse old headers.

Change-Id: Iafec080f99c67560974e9ebc0cbfb27d9a4b2d6f
Reviewed-on: http://codereview.qt-project.org/5755
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>