Remove Backend Implementation of sast_reports_in_inline_diff Flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/141909



Merged-by: Allen Cook <acook@gitlab.com>
Approved-by: Allen Cook <acook@gitlab.com>
Reviewed-by: Jannik Lehmann <jlehmann@gitlab.com>
Reviewed-by: Ahmed Hemdan <ahemdan@gitlab.com>
Co-authored-by: Jannik Lehmann <jlehmann@gitlab.com>