Retain Git trailers by default during cherry-picking
What does this MR do?
- This feature has worked well for the past few patch releases, and is therefore considered stable
- This removes said feature flag which enables this code path by default
- After merge, the feature flag
cherry_pick_trailers
should be removed where defined
Author Check-list
- [-] Has documentation been updated? n/a
Closes: https://gitlab.com/gitlab-org/release-tools/-/issues/501