We no longer support fake fullscreen mode on macOS, and haven't for
a long time.
Pick-to: 6.7 6.5
Change-Id: Ic2eb6065239c4e5be5ab2011a6da50272c77460a
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 4079ecfb9b3dc794212a81154e18145256741cfd)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>