Merge branch 'el-cleanup-telesign-callback-ff' into 'master'

Remove telesign_callback feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/128463



Merged-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Approved-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Approved-by: Joseph Wambua <jjoshua@gitlab.com>
Co-authored-by: eugielimpin <elimpin@gitlab.com>