Clean up any unassociated DeployToken records

As a follow up to #212523 (closed), there was a short period in which deleting a ProjectDeployToken or GroupDeployToken using the deploy token API, would result in the associated DeployToken record not being deleted. This issue is meant to clean up any orphaned DeployTokens from that period.

This will require a migration that goes through deploy_tokens records, and checks to see if they are or are not associated with any project or group deploy token records, removing them if they are not.