Add an Interaction model without a Verifier

[ericvoit]

In April, Vinnie asked for an interaction model which doesn't require a Verifier. This is for things like SGX where the provable identity of the MRSIGNER is sufficient to the Relying Party. The specific comment was: The question then is whether we need some form of time interval tracking between Verifiers A & B. I believe it to be useful to understand the delta in time between the creation of the original Attestation Results, and their receipt on the Relying Party. The one time I can think of when this might not be necessary is when the Relying Party trusts that the Attester cannot be meaningfully changed from the outside over time. (E.g., a specific MRENCLAVE can expose no changing Evidence to Verifier A over time, and this MRENCLAVE is trusted to be unable to mimic another MRENCLAVE or replay Attestation Evidence about another MRENCLAVE.) In such a case, nonce#2 from figure 1 can be safely dropped. I will propose text to this effect into the draft.