In certain cases where the device has been misregistered and cannot be deleted from the portal, it may need to be removed via SQL script. To do so, use the script below. The DEVICEID variable is the ID of the device to be deleted.
delete from IdExchange.Device where DeviceId='DEVICEID'
delete from IdExchange.DeviceRequests where DeviceId='DEVICEID'
delete from IdExchange.DeviceEncodingRequest where DeviceId='DEVICEID'