Remove legacy Quay release automation

[Arcticae]

Delete the obsolete Quay CD workflows and their Nix CI shell now that releases use the GCP workflow introduced by the baseline PR. Remove the stale CODEOWNERS file as part of retiring the old repository automation.

Summary

Testing strategy

[Arcticae]

This change is part of the following stack:

• Add Starkstream GCP image release workflow #6
  • test: pin upstream etcd container image #17
    • Prune DNA to Starknet-only functionality #7
      • Rename Rust packages and binaries to Starkstream DNA #8
        • Remove legacy Quay release automation #9 ◀
          • Revamp Starkstream DNA documentation #10

_{Change managed by git-spice.}