Remove Mac visibility workaround on Qt 5.
Remove Mac visibility workaround on Qt 5.

WA_DontShowOnScreen now works the same way on all
platforms.

Change-Id: If7c5416e4f38b4c5ac955c861aad5b1ee55aef05
Reviewed-by: Morten Johan Sørvig <84fe11dd8bf63b99760f9a020e6b4a145681baec@nokia.com>

drgvond/qtquickcontrols,richardmg/qtcomponents,drgvond/qtquickcontrols,drgvond/qtquickcontrols,mizukusak/qtquickcontrols,jfaust/qtquickcontrols,kobolabs/qtquickcontrols,mizukusak/qtquickcontrols,richardmg/qtcomponents,richardmg/qtcomponents,jfaust/qtquickcontrols,kobolabs/qtquickcontrols,mizukusak/qtquickcontrols,jfaust/qtquickcontrols,kobolabs/qtquickcontrols