original `py` is not maintained anymore


https://github.com/pytest-dev/py is getting dust nowadays,
please rewrite the tests without requiring this unmaintained tool.

```
$ grep 'import py$' -r 
tests/test_doctests.py:import py
tests/test_actual_test_runs.py:import py
```

I'm busy slowly removing it's use from Debian before it's removed altogether, at last
https://tracker.debian.org/pkg/python-py