Merge branch 'pb/439075/remove-hamilton-feature-flag' into 'master'

Remove references to hamilton_seat_management feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/156961



Merged-by: Jessie Young <jessieyoung@gitlab.com>
Approved-by: Bishwa Hang Rai <bhrai@gitlab.com>
Approved-by: Jessie Young <jessieyoung@gitlab.com>
Reviewed-by: Bishwa Hang Rai <bhrai@gitlab.com>
Reviewed-by: Paulo Barros <pbarros@gitlab.com>
Co-authored-by: Paulo Barros <pbarros@gitlab.com>