Merge branch 'sk/remove-dead-code' into 'master'

Remove unused code in merge_request model

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143990



Merged-by: Rutger Wessels <rwessels@gitlab.com>
Approved-by: Dominic Bauer <dbauer@gitlab.com>
Approved-by: Rutger Wessels <rwessels@gitlab.com>
Co-authored-by: Sashi Kumar <skumar@gitlab.com>