Unregistering GenericSetup import steps

[Fabio Corneti]

Hi all,
during the lifecycle of a Plone 2.5.3 installation we have removed a  
gs based product, but I still can see the registered import steps in  
portal_setup.

Is it possible to deregister a "dead" import step? I've looked at gs  
source code but cannot find methods for doing this besides editing  
directly the _registered dictionary in the import registry (which  
looks dangerous).

Best,
Fabio Corneti