Session printers created via policy in Citrix XenApp are considered local printers. As such they are in the registry key that is common for local printer definitions. That registry key location on Windows 2008 R2 is :
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print\Printers
Problem with session printers such as additional printers appearing in the user's list of available printers while in a session, most often is a result of driver corruption. Once the corrupt driver has been fixed or removed, you may have printers still showing up in user sessions that do not belong.
One of the things you can check is the key in the registry where the session printers are defined.
For stuck printers, as option to get rid of them is often to delete the users profile but that's not always the best option so removing the session printers defined for that user can be done through the registry. Be cautious when removing but when there are no users logged into the Cirix Xenapp server, there should be no session printers defined.
