Remove the use_only_onboarding_status_db_value feature flag
What does this MR do and why?
- accept the code it is blocking as that is our next step and we only used the feature flag to de-risk. This has been enabled on production for at least 2 weeks without issue https://gitlab.com/gitlab-org/gitlab/-/issues/454680#note_1894392925 and this area only executes on GitLab.com.
- see decision about users who were in onboarding before use of db values to drive it in #435745 (comment 1839940950)
- see https://gitlab.com/gitlab-org/gitlab/-/issues/454680
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #454680
Edited by Doug Stull