[Distributed] deleteKey support for HashStore (#46049)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46049
Adding support for the deleteKey API in the c10d HashStore.
ghstack-source-id: 113874207
Test Plan:
Added C++ tests to check whether deleteKey function works, and
whether it returns an exception for attempting to delete non-existing keys.
Reviewed By: jiayisuse
Differential Revision: D24067657
fbshipit-source-id: 4c58dab407c6ffe209585ca91aa430850261b29e
