The package-maps install of tox is only defined for gentoo, and that
came in with the original image build parts. We don't need that any
more.
10-pip-packages I didn't trace down, but it hasn't been doing anything
for a long time, since we removed pip-and-virtualenv. We can remove
that.
The install done in 40-install-tox I can not see being used anywhere.
It came in with If5397d731e9fb04431482529aed23cd9fdaecc1d but I can't
see the venv actually referenced anywhere. I think this has all been
replaced by the ensure-tox role (or, indeed, jobs migrating away from
tox). Remove it.
Change-Id: If3fddd79dde56f4087e465ed8b8013f0f337e0cb
75a6a641b1