Merge branch '370608_cleanup_rely_on_protected_branches_cache_ff' into 'master'

Cleanup 'rely_on_protected_branches_cache' feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/112865



Merged-by: Etienne Baqué <ebaque@gitlab.com>
Approved-by: Tymm Schmitke <tschmitke@gitlab.com>
Approved-by: Etienne Baqué <ebaque@gitlab.com>
Co-authored-by: Vasilii Iakliushin <viakliushin@gitlab.com>