Remove _dynamic_tied_weights_keys
* No need to check _dynamic_tied_weights_keys and no need for
recursion
* Updated an error message that mentioned _dynamic_tied_weights_keys
* Removed a test that involved _dynamic_tied_weights_keys
The attribute is still referenced in the custom tie_weights method of
musicgen and musicgen_melody, but my understanding is that the custom
method will be removed anyway, so I left it there.
