Revert D24481801: Optimize backward for torch.repeat
Test Plan: revert-hammer
Differential Revision:
D24481801 (https://github.com/pytorch/pytorch/commit/4e6f2440d84a77bd251b7d7e573b0b33e4f3fe5c)
Original commit changeset: 95c155e0de83
fbshipit-source-id: 0fb0afde760b0f5e17bd75df950a5d76aee5370b
