The KWindowSystem change 32526718eae99ccb594360627586eebdf793372b caused
a regression in KWin as Qt::Enter on keypad is no longer enter, but enter
with modifier mask. For all other modifiers it was never a problem that
the KKeyServer method also returned modifiers as it could not read the
X modifiers anyway.

As KWin has full knowledge about the modifiers through Xkb it does not
need the modifier mapped into the Qt::Key.

This fixes the failing TestWindowSelection autotest which started to fail
due to the change in KWindowSystem.