Bug#568895: user-setup: Remove some of the default groups, they are unused now

[Frans Pop <elendil@planet.nl>]

On Monday 08 February 2010, Frans Pop wrote:
> However, user-setup should remain backwards compatible with Lenny. That
> could be implemented in different ways [1], but it does mean we cannot
> just remove the groups.

Also, users only get added to groups that actually exist at the end of the 
installation (which depends on which packages have been installed).
So there's no real problem with leaving obsolete groups listed in the 
default setting for backwards compatibility.