Revert D24002415: Some fixes to smooth_l1_loss
Test Plan: revert-hammer
Differential Revision:
D24002415 (https://github.com/pytorch/pytorch/commit/fdbed7118e8501f20568020afe5ebb00e4b97e49)
Original commit changeset: 980c141019ec
fbshipit-source-id: 8981b5f6d982ed66c670122e437540444cb5f39c
