Draft: Ignore shared_runners related columns for namespace and project

What does this MR do and why?

This is a MR:

• Remove the code referencing the columns to drop
• Ignore the columns to drop as described at https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#dropping-columns

Columns to drop are:

• namespace_statistics.shared_runners_seconds and namespace_statistics.shared_runners_seconds_last_reset
• project_statistics.shared_runners_seconds and project_statistics.shared_runners_seconds_last_reset
• namespaces.last_ci_minutes_notification_at and namespaces.last_ci_minutes_usage_notification_level

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #277452