Revert "[3/n] Thread PG: add threaded PG implementation (#88627)"
This reverts commit 6dd081846e3ae6192b375d658d4b4f3d6bd9df6e.
Reverted https://github.com/pytorch/pytorch/pull/88627 on behalf of https://github.com/huydhn due to This breaks one macos m1 test https://hud.pytorch.org/pytorch/pytorch/commit/6dd081846e3ae6192b375d658d4b4f3d6bd9df6e in trunk. PR also fails with the same issue so I think trymerge code has a bug here letting this one merged
