Remove create_cross_project_pipeline_worker_rename FF

What does this MR do and why?

Removes the create_cross_project_pipeline_worker feature flag. The actual worker removal will be handled in a subsequent release.

The feature flag still

Related #341410 (closed)

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.