Remove reference to quantum cli in provider network extension
Remove reference to quantum cli in provider network extension

We don't need this info in the doc string as it is already in the admin
guide. If the CLI changes then we'll also have to update the doc string.

Fixes bug 1195429

Change-Id: If27788477c886f6faedbc5fca7856b683a6953f1

gkotton/vmware-nsx,gkotton/vmware-nsx