Revert D27978269: Smart Decay for Adam - Caffe2
Test Plan: revert-hammer
Differential Revision:
D27978269 (https://github.com/pytorch/pytorch/commit/aaa1e07609b847cb8ec8d93cea1cb0ac51d32f4c)
Original commit changeset: e47524101ddf
fbshipit-source-id: 334824bbf9a6ed788e75af9c292754081f70a19b
