Merge branch 'el-cleanup-arkose-labs-oauth-signup-challenge-ff' into 'master'

Remove arkose_labs_oauth_signup_challenge feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145225



Merged-by: Eugie Limpin <elimpin@gitlab.com>
Approved-by: Juliet Wanjohi <jwanjohi@gitlab.com>
Approved-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Approved-by: Aboobacker MK <akarakath@gitlab.com>