Hi,
Afaik, things only appear in "User Catalog" (the service catalog of a user group) when a shortcut has been actively placed there. Thus, going to Explorer -> User catalog and removing the shortcut from the group's sub folder will remove the item from the catalog.
You may need a Tomcat restart and/or cache cleaning though, I distinctly recall a caching issue with this that I never got around to fully investigate.
Hth,
Carsten