Finish removal of AT_CHECK, officially deprecate the macro. (#20600)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20600
All future uses of AT_CHECK will fail our CI.
Reviewed By: jerryzh168
Differential Revision: D15375397
fbshipit-source-id: 5582664d6c7c4f1a56ae45647eb1bca49fed2866
