Revert "Update shallow_copy_and_detach for nested tensor impls to enable nested tensor softmax backward (#81838)"
This reverts commit 6697f1e467cc8d4dfaf66c1d5a451e2bf82cf588.
Reverted https://github.com/pytorch/pytorch/pull/81838 on behalf of https://github.com/osalpekar due to Reverting this in order to revert https://github.com/pytorch/pytorch/pull/80981 cleanly. That diff caused GPU Inference breakage internally
