expander: don't handle hover state manually
expander: don't handle hover state manually

MxWidget can now take care of the hover state.

pwithnall/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx