Revert "search buffers for dtype"
Reverts huggingface/transformers#23159

This breaks the FDSP integration for some reason, so reverting for now as we investigate things further. The revert will be included in the patch 4.29.1

(Test that breaks:
```
RUN_SLOW=yes pytest -s -v tests/fsdp -k test_checkpointing
```
in Accelerate)
_The documentation is not available anymore as the PR was closed or merged._