[Gradient Compression] Remove unnecessary warning on the rst file and the check on C++ version (#58170)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58170
Now comm hook can be supported on MPI and GLOO backends besides NCCL. No longer need these warnings and check.
ghstack-source-id: 128799123
Test Plan: N/A
Reviewed By: agolynski
Differential Revision: D28388861
fbshipit-source-id: f56a7b9f42bfae1e904f58cdeccf7ceefcbb0850
