Rename PythonUDF{Call,Resp} (#27530)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27530
Per discussion in #27286, the `UDF` part is superfluous.
This makes the naming consistent with the `MessageType` enum.
Test Plan: Imported from OSS
Differential Revision: D17808211
Pulled By: pietern
fbshipit-source-id: 0ff925de26d027951ce285750ad276ed17fee4c6
