Merge branch 'aqualls-clean-out-flag' into 'master'

Docs: remove final mentions of moved_mr_sidebar flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149348



Merged-by: Phillip Wells <pwells@gitlab.com>
Approved-by: Phillip Wells <pwells@gitlab.com>
Co-authored-by: Amy Qualls <aqualls@gitlab.com>