Revert D25511543: [Gradient Compression] Implement the original layerwise PowerSGD
Test Plan: revert-hammer
Differential Revision:
D25511543 (https://github.com/pytorch/pytorch/commit/71f3399e19dd0e48b3360e0b973803ea408c315a)
Original commit changeset: 19ef188bc2d4
fbshipit-source-id: a363641a059aeacc57684884998cf8fb7363d748
