Deprecate Flax support (#12151)
* start removing flax stuff.
* add deprecation warning.
* add warning messages.
* more warnings.
* remove dockerfiles.
* remove more.
* Update src/diffusers/models/attention_flax.py
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>
* up
---------
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>
