efl_ui: fix not to call _on_child_del() after container is deleted

efl_ui: fix not to call _on_child_del() after container is deleted

If efl_ref() is called to child, then child may not be deleted when
container is deleted.
This causes _on_child_del() is called after container is deleted and it
causes crash if container data is accessed in _on_child_del().

To resolve the above issue, all callbacks of child are deleted not to
call _on_child_del() after container is deleted.