Revert "Added serialization to postlocal_SGD. (#80435)"
This reverts commit dfdf4e79df2056fe092a3d28e903367fb8a624b6.
Reverted https://github.com/pytorch/pytorch/pull/80435 on behalf of https://github.com/suo due to broke distributed tests on trunk, see: https://hud.pytorch.org/pytorch/pytorch/commit/dfdf4e79df2056fe092a3d28e903367fb8a624b6
