I'm going to run with the approach of adding a private _uninstall function in ensurepip (that includes the version guard), and then a "python -m ensurepip._uninstall" submodule to invoke it from the command line.

I'll also extend the with_pip test in test_venv to cover uninstallation (it won't be a venv feature, it's just a convenient way to test that the uninstall command actually does the right thing).