DeleteOrphanedIssueLabels looks through the database for issue_labels where the label no longer exists and deletes them.

RemoveInvalidLabels looks through the database to look for comments and issue_labels that refer to labels do not belong to the repository or organization that repository that the issue is in.

OAuth2Grant here is a snapshot of models.OAuth2Grant for this version of the database, as it does not appear to have been added as a part of a previous migration.