efl_canvas_scene: rename event from focus,* to scene_focus,*
This event can just be renamed, no need to handle legacy. The reason for
this, that this event is used to map to EVAS_CALLBACK_ enum fields,
which means, the legacy names of the event does not matter.
Reviewers: cedric, segfaultxavi, zmike, stefan_schmidt
Reviewed By: zmike
Maniphest Tasks: T7476
Differential Revision: https://phab.enlightenment.org/D8242