Revert "Ported hardtanh decomposition to ref (#78689)"
This reverts commit 484282a6fdafe647aaac05e33771740ff22b4430.
Reverted https://github.com/pytorch/pytorch/pull/78689 on behalf of https://github.com/kit1980 due to test_meta_nn_functional_hardtanh_cuda_float32 failed on both PR and trunk, see https://hud.pytorch.org/pytorch/pytorch/commit/484282a6fdafe647aaac05e33771740ff22b4430
