Whenever possible python packages should use pip

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (```recipe```) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For **recipe**:

* Whenever possible python packages should use pip. See https://conda-forge.org/docs/maintainer/adding_pkgs.html#use-pip

_Originally posted by @conda-forge-linter in https://github.com/conda-forge/setuptools_subversion-feedstock/issues/6#issuecomment-757381293_