Avoid unnecessary locks on internal_ids (remove feature flag)

What does this MR do?

This MR removes the feature flag iid_always_track to permanently enable the behavior from !17123 (diffs). This avoid unnecessary locks on internal_ids when the IID hasn't actually changed.

In this case, iid_always_track: false is the desired new behavior.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry

Performance and Testing

The unnecessary locks dropped completely (red line).