Remove any usage of greylist repo from the pipeline

All open hardening_manifest MRs: https://repo1.dso.mil/groups/dsop/-/merge_requests?label_name%5B%5D=hardening_manifest.yaml+migration

• Create Draft MR for removing all greylist usage (merge on Friday 2/26/21)
• Delete GREYLIST_BACK_COMPAT from dsop group CI variables (delete on Friday 2/26/21)
• Remove all usage of the greylist from the pipeline
  • check cves -- pipeline_wl_compare.py
  • csv output -- pipeline_csv_gen.py
  • preflight -- metadata.py
  • everything in hardening_manifest_yaml folder (might want to archive these files) @james.petersen
• folder_structure.sh in preflight should check for deprecated files and existing hardening_manifest.yaml
• Update documentation to no longer mention usage of the greylist
  • README.md
  • pipeline_csv_gen.py
  • pipeline_wl_compare.py