Deprecate chain_matmul (#57735)
Summary:
This one's easy. I also included a bugfix.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57735
Reviewed By: bdhirsh
Differential Revision: D28318277
Pulled By: mruberry
fbshipit-source-id: c3c4546a11ba5b555b99ee79b1ce6c0649fa7323
