I cannot find any articles on the subject, but from what I recall, there is a "Delete" button within the AD Config tab of the SEEMS Configuration Wizard. What I can;t recall is if this deletes just the AD Sync config, or if it will delete the computer records from the AD tables or not.
Pending some official documentation, perhaps take a DB backup and give it a whirl?
Another unsupported option whould be to locate and delete the contents of the dbo.ADComputers table. Again, this is from memory so backup and perform at your own risk!