Remove preload_max_access_levels_for_labels_... FF

What does this MR do and why?

This MR removes the preload_max_access_levels_for_labels feature flag which was enabled by default in %15.11.

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 #390664 (closed)