Once we've settled on a max-servers value of 0 without any servers this
is the nextstep in removing the provider. This should completely remove
the provider from the launcher and the image builders.
We keep the airship-citycloud nodepool provider for historical
information purposes. We can clean this up later.
Change-Id: Icfb8fc6d2b15714ecb58960d8e44b199bedd6b0d