Merge branch '451208-remove-ambiguous_ref_modal-flag' into 'master'

Cleanup the ambiguous_ref_modal feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149641



Merged-by: John Mason <9717668-johnmason@users.noreply.gitlab.com>
Approved-by: Moaz Khalifa <mkhalifa@gitlab.com>
Approved-by: John Mason <9717668-johnmason@users.noreply.gitlab.com>
Reviewed-by: Moaz Khalifa <mkhalifa@gitlab.com>
Co-authored-by: j.seto <jseto@gitlab.com>