No need to install a lot of junk just to have tox make a new venv and install
things into it.  And then ci.pip can be much smaller, installing just what kits
need: kit.pip

auditwheel only installs on Python 3.  So only install it where we need
it, and clean up other .pip files along the way.

This required pinning setuptools more aggressively, and cleaning up some
dependency sloppinesss.