Clean up `SafelyChangeColumnDefault` for `allow_runner_registration_token` columns
In !150648 and !150562 (merged), we changed the column defaults, following the procedure stipulated in https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#changing-column-defaults. In %17.1, we should clean up the SafelyChangeColumnDefault
usages.