Default enable linear_group_descendants_finder_upto

What does this MR do and why?

Default enable linear_group_descendants_finder_upto. This feature flag has been enabled for all actors for many months.

How to set up and validate locally

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

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 #350972 (closed)