Remove partially initialized Tensor in Deserialization (#14197)

Remove partially initialized Tensor in Deserialization (#14197)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14197

Pull Request resolved: https://github.com/pytorch/pytorch/pull/13642

Previously we pass in a patially initialized Tensor to Deserialize and it will fill
it with the result of deserialization of a tensor proto. Now we want it to return
a Tensor directly since it's just a shared pointer to TensorImpl.

Reviewed By: dzhulgakov

Differential Revision: D12874357

fbshipit-source-id: 12b80a763375da23cfa64a74d6bc186d8d03b94f