Summary:
The old `torch.distributed` will go to `torch.distributed.deprecated`
The old DDP will go to `torch.nn.parallel.deprecated`
Now `torch.nn.parallel.DDP` will use c10d DDP
Now `torch.distributed` will use C10d frontend API
Pull Request resolved: https://github.com/pytorch/pytorch/pull/11405
Reviewed By: pietern
Differential Revision: D9733733
Pulled By: teng-li
fbshipit-source-id: d6a3f3e73f8d3a7fcb1f4baef53c78063b8cbb08