Remove 'nova-cells' service

We're going to start unpicking this stuff from the top down. Start with
the 'nova-cells' executable itself.

Part of blueprint remove-cells-v1

Change-Id: I5bd1dd9f1bbae7a977ab9e032c4f4d200c35e193
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

setup.cfg

@@ -57,7 +57,6 @@ console_scripts =
     nova-api = nova.cmd.api:main
     nova-api-metadata = nova.cmd.api_metadata:main
     nova-api-os-compute = nova.cmd.api_os_compute:main
-    nova-cells = nova.cmd.cells:main
     nova-compute = nova.cmd.compute:main
     nova-conductor = nova.cmd.conductor:main
     nova-console = nova.cmd.console:main