e_comp_wl: fix cursor flickering when mouse_out occurs

e_comp_wl: fix cursor flickering when mouse_out occurs

Showing and hiding a cursor is request-triggered operation by clients.
Hiding a cursor when mouse_out occurs is unnecessary server-side operation
and causes cursor flickering when mouse moves between apps.

Scenarios:
1. When mouse moves between cursor-supported apps (App 1 & App 2), App 2
sets its cursor and E20 hides an old cursor and shows a new one.

2 When mouse moves from a cursor-supported app to a cursor-unsupported app,
the cursor-unsupported app sets its cursor as null and E20 hides a cursor.

Change-Id: I3e15fd821064aa819f93eaed664c7d700a46b05a