Revert D25097324: [pytorch][PR] [ONNX] Cast Gather index to Long if needed
Test Plan: revert-hammer
Differential Revision:
D25097324 (https://github.com/pytorch/pytorch/commit/55fc0e9e534d9141fcac08e9ab42df39e24a5274)
Original commit changeset: 42da1412d1b9
fbshipit-source-id: 491994a35a8aaf207dd5905191847171586aa4b7
