Revert "[_shard] make ShardedTensor be a Tensor and nn.Parameter (#79825)"
This reverts commit 9c32439a770845793107a584f17f4da70ccb5df0.
Reverted https://github.com/pytorch/pytorch/pull/79825 on behalf of https://github.com/janeyx99 due to Sorry, reverting for breaking multigpu tests https://hud.pytorch.org/pytorch/pytorch/commit/9c32439a770845793107a584f17f4da70ccb5df0
