Removing ci_active_pipelines from table plan_limits

What does this MR do and why?

Removing ci_active_pipelines from table plan_limits

Column has been ignored as of #408141 (closed)

Following: https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html#the-removed-column-has-no-indexes-or-constraints-that-belong-to-it

Screenshots or screen recordings

N/A

Before	After

How to set up and validate locally

Migrate locally and column should be removed

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 #414750 (closed)