Remove reference to property `verifiedDIDList` deleted 6 months ago.

Created by: absoludity

The property verifiedDIDList was removed during the initial development of the DIA after @PatStLouis recommended sticking with just the credentialSubject.id . This reference remained and confuses readers (like me :) ).

One related question (not blocking this PR): AIUI, the subject of the DIA should be the DID of the issuer of the DPP/DCC (as outlined originally in https://github.com/uncefact/spec-untp/issues/56 but also now in the did:webvh spec). Although we are doing so here by ensuring the DIA.credentialSubject.id is the did of the DPP/DCC issuer, we also appear to be mixing types. That is, in the DPP, the issuer did is a CredentialIssuer, whereas here in the DIA, the same id has a type RegisteredIdentity. These two types have different properties, for example, RegisteredIdentity has the registrationScopeList. So when putting the data together in a graph, we'll get a single node which has multiple types. It's not clear to me whether this may be an issue later down the track.

My initial thought was that the DIA credentialSubject should be a CredentialIssuer, which would work for three of the other properties currently on RegisteredIdentity (name, registeredId and idScheme, which are all part of the CredentialIssuer.alsoKnownAs), but not registerType nor registrationScopeList, which really sound like properties of the registration organisation's DID and the certifier DID respectively? (That is, the DIA issuer's DID, would have some way of getting that the register type, rather than including it in the DIA for the UNTP DPP/DCC, while, for example, a DCC issuer's DID would have some way of proving the scope that they are allowed to attest). It seems that the DigitalIdentityAnchor is trying to be used for more than identity anchoring, which may need to be split out longer-term.