Make remaining RRef methods return futures (#57860)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57860
The other methods for RRefs just did bookkeeping and are trivially easy to migrate to Futures (which is done mainly for consistency at this point).
ghstack-source-id: 129567068
Test Plan: CI
Reviewed By: mrshenli
Differential Revision: D28286175
fbshipit-source-id: 1d97142803f73fe522435ca75200403c78babc68
