Remove Application/cbor-diagnostic

[mkhraisha]

https://w3c.github.io/vc-jose-cose/#example-a-simple-example-of-a-verifiable-credential-secured-with-cose

Remove the application/cbor-diagnostic header from the spec as it appears to be incorrect.

[mkhraisha]

@msporny lmk what I can do to help out with this, I don't believe I have access to any respec config/build , it seems the most I can do is modify things in this repo.

[msporny]

The issue is with this code block

https://github.com/w3c/respec-vc/blob/main/src/cose.js#L87-L125

Once that is commented out or removed we would need to make a new release of respec-vc and then use that new version in the vc-jose-cose spec.