Revert D20518647: [pytorch][PR] [C++ API Parity] [Optimizers] Merged Optimizer and LossClosureOptimizer
Test Plan: revert-hammer
Differential Revision:
D20518647
Original commit changeset: 4760d1d29df1
fbshipit-source-id: b84f1a06c2de27e147716279223a6844ef89f760
