you can just manually remove those channels that do not have a matching entry anymore in the services tab of the dvb adapter.
At the moment there is no way to scan for channels that are defined, bit are not mapped in the services tab. I am not sure what happens if you rerun the "Map DVB services to channels..." function. I suspect that is only adds the new channels but keeps the old channels in place.
It should be relatively easy to create a function that could scan the channels to see if there are unmapped channels and then ask what to do with it.
(you could make this a feature request)
Not sure if a channels should be automatically removed if the service is no longer available. Maybe there is a problem or something else that has caused the service to be removed.
Hein