Hi Roger
When a user is assigned to a certification a certification completion record is created and this appears on a users Record of Learning whether they have completed this or is hidden.
Unassigning the user from the Certification does take it from the ROL if the Learner has made no progress but if they have completed this then this still appears on the ROL.
There is a Certification completion editor that will let you change the record for each user. If you change the status of the user to 'No progress' and then unassign the user from the certification then in theory their ROL record should no longer show.
Can you test this out on a user to see if this works for you.
The other way to make the Certification not show on any users ROL is to delete the Certification under manage Certifications. This is undoable so you need to make sure that there are no users that you want to keep Certification completion records for. A backup should be done in just to make sure you can restore records if something unexpected happens.
regards