gtkmain: Do not try to coalesce/ignore crossing events

gtkmain: Do not try to coalesce/ignore crossing events

Under grabbing circumstances we used to get several crossing events,
some corresponding to the grab itself and some corresponding to
pointer motion.

The backends now do a better job at keeping those simple, which
means we sit listening for events that don't actually arrive. This
triggers pointer focus issues when dragging windows or opening
grabbing popups.

Actually obey those events, they will be the only ones we get now.