MetaCursorRenderer: Rely on update_cursor for redrawing

Calling queue_redraw() in _force_update() is not needed because
update_cursor() will do this when needed, i.e. when switching between
hardware cursor and texture cursor, or when drawing with texture cursor.

There is also no need to force _native_force_update() because
update_cursor() will cover this as well when needed. When not changing
cursor but only the gbm_bo, the "dirty" boolean on the gbm_bo will
trigger a redraw.

https://bugzilla.gnome.org/show_bug.cgi?id=744932