I recently moved from one state to another. In the state I moved out of, they don’t seem to have any procedures or forms for un-registering to vote.
The illegality is not in being registered in two places; it is in VOTING in two places.
When I lived in the heavily Democrat New Orleans area, the Registrar periodically sent me a postcard that said, “We are purging our voter registration rolls of voters who may have died or moved away. If you do not receive this card, please contact this office immediately.”
It took real work to get my dead wife off of the voting roles. They will not do it based on actual death records, someone with responsibility has to file the request. If we both had died in an accident, I’m not sure WHO would have had the authority to get the two names removed.
Fortunately my state requires picture ID, so some random democratic woman couldn’t search the death roles and come pretend to be my wife.