Remove unused variable in choose_generation_strategy

Summary:
As reported by an issue in github (facebook#341)
This variable `no_max_parallelism` is not used by `choose_generation_strategy` but is still one of the functions input arguments.
Cleaning it up in this diff

Reviewed By: lena-kashtelyan

Differential Revision: D22576370

fbshipit-source-id: 13c3d41b2c66151508a8d5e1290ff73b0601010f

ax/modelbridge/dispatch_utils.py

@@ -122,7 +122,6 @@ def choose_generation_strategy(
     no_bayesian_optimization: bool = False,
     num_trials: Optional[int] = None,
     num_initialization_trials: Optional[int] = None,
-    no_max_parallelism: bool = False,
     max_parallelism_cap: Optional[int] = None,
     max_parallelism_override: Optional[int] = None,
 ) -> GenerationStrategy: