Remove the ignore rule related to delayed project/group deletion

Why

This issue is a follow-up from Cleanup columns related to delayed project/grou... (#411206 - closed).

We're removing columns from ApplicationSetting and NamespaceSetting class. Since we're following https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html documentation, we have to do it in 3 releases:

• Ignoring the column (release M) ✅
• Dropping the column (release M+1)
• Removing the ignore rule (release M+2) <--- HERE WE ARE