ivi-shell: rework remove_layer notification

ivi-shell: rework remove_layer notification

The add_notification_remove_layer API accepts a simple
wl_listener instead of a ivi-shell specific notification
function. Therefore, the API is renamed to add_listener_remove_layer.

This change has several advantages:
1. Code cleanup
2. No dynamic memory allocation. Listeners are allocated
   by controller plugins
3. Remove API is not needed. Controller plugins can easily
   remove the listener link.

The remove API is removed too:
- ivi_layout_remove_notification_remove_layer

Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>