Remove resize hook from QSGRenderLoop, exposureChanged is enough.

After much back and forth, I think we have settled on the right approach
in QtGui, which is that resizeEvent is pretty much useless as the
action happens on the following exposeEvent().

Change-Id: I5e87bda89853907d041f56acf9a2895e540c41f0
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>