[8/N] Remove c10d/ddp fork tests. (#63454)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63454
Continuation of https://github.com/pytorch/pytorch/pull/63443, this
PR removes all fork tests from torch.distributed.
ghstack-source-id: 136285511
Test Plan: waitforbuildbot
Reviewed By: SciPioneer
Differential Revision: D30387872
fbshipit-source-id: f6d6313db126ae7b95b86f78a1e0726887c5c513
