Merge branch '390361-rollout-parallel-cron-worker' into 'master'

Remove the parallel_bulk_cron_worker feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/113359



Merged-by: John Mason <9717668-john-mason@users.noreply.gitlab.com>
Approved-by: John Mason <9717668-john-mason@users.noreply.gitlab.com>
Approved-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Co-authored-by: Dmitry Gruzd <dgruzd@gitlab.com>