Chore: Remove the ai editor assistant feature flag

See merge request !157837



Merged-by: Tetiana Chupryna <tchupryna@gitlab.com>
Approved-by: Gosia Ksionek <mksionek@gitlab.com>
Approved-by: Tetiana Chupryna <tchupryna@gitlab.com>
Co-authored-by: Nathan Weinshenker <nweinshenker@gitlab.com>