Tensorimpl cleanup try 2 (#72336)
Summary:
This reverts the previous PR and add some comments to make it clear what the intent is.
Also removes some extra static_assert that are not needed (at least for the compilers I tried).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72336
Reviewed By: r-barnes
Differential Revision: D34006722
Pulled By: albanD
fbshipit-source-id: 290fb89a2d2c66a0d1c3651198b31d21216ec230
(cherry picked from commit 76f0aaa76596b566e0d53c0f65c4899f1dc1f614)
