Clean up Python code generation. (#301)
Clean up Python code generation. (#301)

* python codegen - this schema stuff doesn't seem to ever be used
* python codegen - improve type annotation
* python codegen - clean overly defensive code block
common-workflow-language/schema_salad,common-workflow-language/schema_salad,common-workflow-language/schema_salad,common-workflow-language/schema_salad,common-workflow-language/schema_salad,common-workflow-language/schema_salad,common-workflow-language/schema_salad