Revert D20645945: [pytorch][PR] [C++ API Parity] [Optimizers] Merged Optimizer and LossClosureOptimizer
Test Plan: revert-hammer
Differential Revision:
D20645945
Original commit changeset: 383588065bf1
fbshipit-source-id: 6d7bc5676de64e329d9862889f32033c76b4009c
