Remove unused feature-highlight code

What does this MR do and why?

Part of &11875. This "feature hightlight" was not migrated to the new navigation. It was only used for Kubernetes clusters 6 years ago.

Screenshots or screen recordings

No visual change.

How to set up and validate locally

Search for any code related to feature-highlight and make sure it is all gone.

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.