Use snake names for all files in distributed.rpc (#24502)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24502
Files in distributed.rpc package mixes snake camel names. This
commit cleans that up and all files use snake names now.
ghstack-source-id: 88548990
Reviewed By: xush6528
Differential Revision: D16860155
fbshipit-source-id: 3a22a89bf6c4e11aac5849564fc53296a04d6a8b
