[webauthn] CTAP/U2F doesn't status indicating the user cancelled the operation

AngeloKai has just created a new issue for https://github.com/w3c/webauthn:

== CTAP/U2F doesn't status indicating the user cancelled the operation  ==
In the authenticator parallel processing section (https://github.com/w3c/webauthn/blob/master/index.bs#L738), it says: 

`        :   If any |authenticator| returns a status indicating that the user cancelled the operation,
        ::  1. [=set/Remove=] |authenticator| from |issuedRequests|.
            2. [=set/For each=] remaining |authenticator| in |issuedRequests| invoke the [=authenticatorCancel=] operation on
                |authenticator| and [=set/remove=] it from |issuedRequests|.
`

Looking at both CTAP and U2F specs, I haven't found an error matching this indication. Should we remove this from the algorithm? 

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/658 using your GitHub account