Gitlab Rails [%16.7] : Remove category column from service_access_tokens

Following https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#dropping-columns

In Gitlab Rails: Consolidate SaaS mechanism for is... (#426950 - closed) we added the ignore rule for the category column for service_access_tokens table

In %16.7 we should remove the column