[7/N] Remove fork tests for RPC. (#63443)

[7/N] Remove fork tests for RPC. (#63443)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63443

After https://github.com/pytorch/pytorch/pull/63442, all distributed
tests can run with opt-asan. As a result, we can now remove all of our fork
based tests.

This is the first PR in a stack, which first removes fork based tests from RPC.
ghstack-source-id: 136177744

Test Plan: waitforbuildbot

Reviewed By: lw

Differential Revision: D30384905

fbshipit-source-id: 86d438aebaa6cb02ae2a966fea244849849a1889