[V5] Return a BatchEncoding dict from apply_chat_template by default again (#42567)
* Flip the default return type for `apply_chat_template` to match the underlying tokenizer
* Remove test_tokenization_for_chat tests, which no longer do anything useful
* Remove test_tokenization_for_chat tests, which no longer do anything useful
* Fix test_encode_message tests
* Fix test_encode_message tests
* nit fix
* Trigger tests
* Remove test_tokenization_for_chat
* make fixup
* Add a little test to make sure that doesn't happen again
* make fixup