Check column removals in review

doc/development/database_review.md

@@ -101,6 +101,7 @@ and details for a database reviewer:
   - Check consistency with `db/schema.rb` and that migrations are [reversible](migration_style_guide.md#reversibility)
   - Check queries timing (If any): Queries executed in a migration
     need to fit comfortably within `15s` - preferably much less than that - on GitLab.com.
+  - For column removals, make sure the column has been [ignored in a previous release](https://docs.gitlab.com/ee/development/what_requires_downtime.html#dropping-columns)
 - Check [background migrations](background_migrations.md):
   - Establish a time estimate for execution on GitLab.com.
   - They should only be used when migrating data in larger tables.