Original bug report: https://bugzilla.gnome.org/show_bug.cgi?id=633652
"Google's roster extensions do have an attribute for “don't show this contact”,
but we don't use it. (Nor does Pidgin.)
We don't show Google Talk contacts which have subscription='none', so Gabble
could change its behaviour to make removing from the contact list on Google
Talk actually just remove all subscriptions, not actually delete the contact.
This would be consistent with our existing GTalk special cases, which match
those in Pidgin (which were added by a Google Talk server developer)."