Remove elasticsearch_use_traversal_id_optimization flag

What does this MR do and why?

Removes the elasticsearch_use_traversal_id_optimization feature flag that has been enabled in staging and production and running without issue for a week.

Closes [Feature flag] Rollout of `elasticsearch_use_tr... (#391286 - closed)

Screenshots or screen recordings

N/A

How to set up and validate locally

Same as !108135 (merged)

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 #391286 (closed)