Remove novnc package from nova-compute.

We only need the static files from upstream novnc, so we will install
them from git.

Not installing novnc also means directories like /var/lib/nova and files
like /etc/nova/policy.json from nova-common are no longer created and
thus must be manually created.

Also we were never running nova-novncproxy, so add that to the
nova-compute element.

Fixes bug #1180239

Change-Id: I24ddc4c7e649c07dd7e197e6ac1d1bc79d42fdef