Change hook_entity_delete() to hook_field_attach_delete()

This patch will change using hook_entity_delete() to using hook_field_attach_delete().

Why is this needed?
Because of this bug:

EntityMalformedException: Missing bundle property on entity of type relation. in entity_extract_ids()

The way to reproduce it:

1. Modules to have installed on a clean Drupal (including their dependencies):
   • Field collection
   • Relation add
2. Create a relation type.
3. Create a content type with relation_add and field_collection fields.
4. Add any field to a newly created field collection (a text field, for instance).
5. Create a node and fill all the fields (relation_add and field_collection ones are important) with any values.
6. Try to delete the node.

How does that fix it?
Well, a little of prehistory. Field collections module deletes its items on entity delete - obvious behaviour. After items are deleted, field collection module invokes entity_save in order to save the entity with unsetting references to those items. That's weird to me, but I can't judge, maybe it has to be so, if it's done.

The problem is that, that Relation module deletes relation entities before this mess with Field collections happens. So, when a relation is deleted, but there is still a reference to it in the field, Field collections module calls entity_save - then we get the mentioned error, while trying to update the relation which has been deleted.

Field collections delete themselves on hook_field_attach_delete(), so we have to do the same after them. That's how it's solved.