Revert D25338250: [pytorch][PR] [BE] Fix signed-unsigned warnings
Test Plan: revert-hammer
Differential Revision:
D25338250 (https://github.com/pytorch/pytorch/commit/6317e0b2f1090ea4189e88557d4ff6656fb758cc)
Original commit changeset: e840618b113b
fbshipit-source-id: dbecb068892dc118f257fe5c50692ede2b2462ca
