[pytorch] get rid of cpp_type_str from pybind codegen (#46977)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46977
Clean up a few TODOs in the new python binding codegen.
Get rid of the _simple_type() hack and the uses of cpp_type_str.
Now python argument type strings and PythonArgParser unpacking methods
are directly generated from the original Type model.
Test Plan: Imported from OSS
Reviewed By: ezyang
Differential Revision: D24589209
Pulled By: ljk53
fbshipit-source-id: b2a6c3911d58eae49c031d319c8ea6f804e2cfde
