remove setuptools from wheelhouse.txt (or bump to later version consistent with layer-basic)

[james beedy]

The pinning of setuptools to an old version breaks other layers when used in conjunction with this layer. Is there something that depends on `setuptools>=19.6,<=20.0`, or can we get it out of there, or possibly pin it to something consistent with layer-basic?

Thanks!

[Tim Van Steenburgh (tvansteenburgh)]

This will be fixed as part of https://github.com/juju-solutions/layer-docker/pull/141/files