base: drop commented part about site-packages in Ubuntu
base: drop commented part about site-packages in Ubuntu

Turned out that since we commented mangling of system-wide Python
packages nothing broke. So let's get rid of that part.

Change-Id: I9e3a4424c584fb14cca50bb0b9392f7227161acc

openstack/kolla,rahulunair/kolla,stackforge/kolla,stackforge/kolla,rahulunair/kolla,stackforge/kolla,openstack/kolla