Revert D31580382: [pytorch][PR] dropout update in autodiff
Test Plan: revert-hammer
Differential Revision:
D31580382 (https://github.com/pytorch/pytorch/commit/eb8138d8860a1d6a92e5681b6cbb9b7b977621b0)
Original commit changeset: 41d15da99bf4
fbshipit-source-id: 59f751ee59602a5fd09c17f8c7565dca5e2beb50
