remove casts to `getter` in python_cpp_function.h (#100065)
remove casts to `getter` in python_cpp_function.h
Summary:
These were triggering the warning `-Wcast-function-type-strict` and
breaking the build on my machine.
Test Plan: Rely on CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100065
Approved by: https://github.com/ezyang
