osg-configure: don't check sponsor

osg-configure checks that the sponsor(s) listed in the Site Information section are valid VO names, which it does by looking at /var/lib/osg/user-vo-map.

We don't have a user-vo-map anymore since the switch to vomsmap auth.
(We have a module called "reversevomap.py" that parses the vomsmap file but I don't think the mapping is correct so we can't use it.)

Drop the sponsor check. The sponsor is only used for $OSG_SPONSOR in the job environment, and grep tells me the pilot doesn't use it.