elm_external: shutdown elm after del callback

elm_external: shutdown elm after del callback

This fixes a crash in edje_inspector as:
- delete callback is called on the object
 --> this unloaded elm
- destructor is called on the object
 --> this did some elm stuff, in particular read the config
     from _elm_config (now NULL).

Instead, shutdown elm after del, during free.

Also reset hash pointer to NULL after free.