Merge branch 'pedropombeiro/374525/remove-ff' into 'master'

Remove runners_finder_all_available feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/101099



Merged-by: charlie ablett - OOO 19-21 October NZDT <cablett@gitlab.com>
Approved-by: Jessie Young <jessieyoung@gitlab.com>
Approved-by: Miguel Rincon <mrincon@gitlab.com>
Approved-by: Zeff Morgan <zmorgan@gitlab.com>
Approved-by: Peter Hegman <phegman@gitlab.com>
Approved-by: Marcel Amirault <mamirault@gitlab.com>
Approved-by: charlie ablett - OOO 19-21 October NZDT <cablett@gitlab.com>
Co-authored-by: Miguel Rincon <mrincon@gitlab.com>
Co-authored-by: Pedro Pombeiro <noreply@pedro.pombei.ro>