Cleaned up some code that 'fixed' an issue with the full screen mode on OS X [ci skip].

This is related to
https://bugreports.qt-project.org/browse/QTBUG-30139. Our ‘fix’ used to
work, except that we would get a message that reads something like:

2013-05-17 14:52:25.991 fullscreen[40864:707] not in fullscreen state

Now, everything seems to be working fine…