Remove rpc fork and dist autograd fork tests from PyTorch repo (#29827)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29827
There are known issues for "fork tests + OMP" in Pytorch, rpc and dist autograd tests use OMP thread pools, this caused rpc fork and dist autograd fork tests to be flaky. So remove these fork tests from PyTorch repo. rpc spawn and dist autograd spawn tests are still running.
Test Plan: unit tests
Differential Revision: D18507384
fbshipit-source-id: 9e239f13850832b4b84724828537f73512f3fca9
