Merge branch '498854-delete-orphan-variables' into 'master'

Delete orphaned pipeline variables

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/169441



Merged-by: Tiger Watson <twatson@gitlab.com>
Approved-by: Max Orefice <morefice@gitlab.com>
Approved-by: Tiger Watson <twatson@gitlab.com>
Reviewed-by: Max Orefice <morefice@gitlab.com>
Co-authored-by: Marius Bobin <mbobin@gitlab.com>