Remove feature flag `optimize_where_full_path_in`

What does this MR do and why?

The optimize_where_full_path_in feature flag has been fully enabled on production since yesterday, 4th Jan 2024, and is now safe to remove.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to #432863 (closed)