[rpc] fix RRef alias annotation (#39933)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39933
Fix rref related alias annotation to ensure it's not getting ebased by
the jit dce.
Test Plan: Imported from OSS
Differential Revision: D22015426
Pulled By: wanchaol
fbshipit-source-id: 3e74d49fa9f88abaf662bde7be5284f01f621b98
