Finalize conversion for FKs targeting p_ci_builds

What does this MR do and why?

The ci_builds table is now a partition of the p_ci_builds routing table, but to finalize the partitioning we need to update all of the foreign keys that target ci_builds to use the routing table instead. This blocks us from adding new partitions to p_ci_builds since the other tables won't be able to enforce the constraints since the records will not be in the ci_builds table.

The foreign keys that we are cleaning up here were added in !121718 (merged), validated asynchronously over the past weekend and validated for self-maned with !122087 (merged). Now we can rename the constraints to the old names and drop the FKs that target ci_builds directly.

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 #414396 (closed)