key attestation example includes iss field that isn't required

[jogu]

The example here:

https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html#appendix-D.1

includes an iss field:

We don't appear to define any meaning for the iss claim in a key attestation so we should probably remove it from the example.

(Pointed out by Stefan Charsley during the current HAIP 1.0 interop)