Revert "reland Hardtanh ref (#78894)"
This reverts commit 823ddb6e87e8111c9b5a99523503172e5bf62c49.
Reverted https://github.com/pytorch/pytorch/pull/78894 on behalf of https://github.com/suo due to this caused unexpected successes on master (lol), search test_python_ref_meta__refs_nn_functional_hardtanh_cpu_bfloat16: https://hud.pytorch.org/pytorch/pytorch/commit/823ddb6e87e8111c9b5a99523503172e5bf62c49"`
