Cleanup columns related to delayed project/group deletion on group level

What does this MR do and why?

Based on the issue, we're removing columns from NamespaceSetting model. The columns to be ignored are:

• delayed_project_removal
• lock_delayed_project_removal

Since we're following https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html documentation, we'll do it in 3 releases:

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

MR acceptance checklist

Screenshots or screen recordings

N/A

How to set up and validate locally

N/A

Related to #411206 (closed)