Revert "ApplicationWindow has the WindowFullscreenButtonHint flag by default"

This reverts commit 29d1b0d209ebb267c5a6ac8402c33892c09b8de6.

This patch caused a regression resulting in QTBUG-35049
and should be reverted until we have a better fix.

Change-Id: I76f9fa9859742a63f33757456c64f70183c76178
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>