[ClutterMozEmbed] Remove idle handler for motion
[ClutterMozEmbed] Remove idle handler for motion

We were needlessly using an idle handler to wait for motion event
acknowledgement and re-sending, when we can just send the event when we
get the acknowledgement. This should cut CPU usage a bit.

clutter-project/clutter-mozembed,clutter-project/clutter-mozembed,clutter-project/clutter-mozembed