Remove track_work_items_activity feature flag
What does this MR do and why?
The flag has been defaulted to enabled for several releases, it should be safe to remove now
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 #352903