Revert "eo: replace composite_objects Eina_List with an array of Eo_Object*"

Revert "eo: replace composite_objects Eina_List with an array of Eo_Object*"

Comp objects are rare, and since we allow using classes as interfaces,
we end up allocating a lot of memory for something we don't even use.
That's why it was a linked list in the first place, and that's why it
should remain a list.

This is almost a complete revert. I reverted the code itself, and the
intent (use of array instead of list), but not the tests, or the new
return value added to comp_detach, which is useful.

This reverts commit ef09ef748924c22074e70b97ebc7726fca1513ec.