Remove feature flag for reference filter

What does this MR do?

Removes feature flag :update_nodes_for_banzai_reference_filter

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

After the flag removal is deployed

• clean up the feature flag by running chatops command in #production channel

Closes #230689 (closed)