Revert D24027761: Update backward definition for more operators and reenable tests in test_ops.py
Test Plan: revert-hammer
Differential Revision:
D24027761 (https://github.com/pytorch/pytorch/commit/7d809f5d8e93cb6d332297ece071083845e30e26)
Original commit changeset: c1f707c2a039
fbshipit-source-id: 30750d2f08886036fb8b2cd0ae51c7732d3b7b19
