A problem shows up with using subclasses of `tff.learning.Model`: after wrapping the model as an EnhancedModel, one cannot access the methods that are specifically defined by the subclass model.

This CL removes the EnhancedModel wrapper used when computing baseline metrics and training personalized models. This makes sure that users can access the full functionality of the model returned by `model_fn`.

PiperOrigin-RevId: 321578480