Back out "[pytorch][PR] Migrate soft_margin_loss from the TH to Aten (CUDA+CPU)"
Summary: Original commit changeset: 9ddffe4dbbfa
Test Plan: ci
Reviewed By: yf225
Differential Revision: D17939581
fbshipit-source-id: 44a3b843bf1e7059fec57b9e3d12ed4886816145
