revert to previous behavior

* Caller should be responsible for ensuring the entity_type gets saved (if necessary)
* The sns:create_topics task therefore needs to save the record
clarify the context of delete_topic

I think it’s helpful to make it clear to the reader that the delete_topic call here only makes sense in the context of a rollback after a create. In this context, a save! call is not necessary. So I’m moving the code straight to the after_rollback config.