Revert D28833086: beef up at::_ops API
Test Plan: revert-hammer
Differential Revision:
D28833086 (https://github.com/pytorch/pytorch/commit/e2129d1c067326efba4eac53255b94af05a45b1b)
Original commit changeset: 55f322a8378c
fbshipit-source-id: e55bf812ec411bb6bee87654f1d65ff10c046106
