Remove **kwargs from prepare_optimizer

Summary:
None of the optimizer classes accept **kwargs, so I am removing **kwargs from perpare_optimizer.

Otherwsie, the current code throws an error when creating a custom PrivacyEngine that takes in additional arguments.

Differential Revision: D67456352

opacus/privacy_engine.py

@@ -111,7 +111,6 @@ def _prepare_optimizer(
         clipping: str = "flat",
         noise_generator=None,
         grad_sample_mode="hooks",
-        **kwargs,
     ) -> DPOptimizer:
         if isinstance(optimizer, DPOptimizer):
             optimizer = optimizer.original_optimizer
@@ -136,7 +135,6 @@ def _prepare_optimizer(
             loss_reduction=loss_reduction,
             generator=generator,
             secure_mode=self.secure_mode,
-            **kwargs,
         )
 
     def _prepare_data_loader(
@@ -396,7 +394,6 @@ def make_private(
             distributed=distributed,
             clipping=clipping,
             grad_sample_mode=grad_sample_mode,
-            **kwargs,
         )
 
         optimizer.attach_step_hook(