Move torch/csrc/utils/hash.h to c10/util/hash.h. (#42503)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/42503
Test Plan: Imported from OSS
Reviewed By: IvanKobzarev
Differential Revision: D23252331
Pulled By: AshkanAliabadi
fbshipit-source-id: 3c4c0e27b9a7eec8560e374c2a3ba5f1c65dae48
