torch._numpy: remove noops and half-implemented nan-functions (#107596)
As discussed in the review of https://github.com/pytorch/pytorch/pull/106211, remove several noops (https://github.com/pytorch/pytorch/pull/106211#pullrequestreview-1559806543 and https://github.com/pytorch/pytorch/pull/106211#pullrequestreview-1559809287).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107596
Approved by: https://github.com/lezcano
