remove the option to return c_nonce from the credential response

[bc-pi]

This only makes sense when/if/after #381 is merged.

Originally posted by @bc-pi in relation to #381 (comment)

Discussed on the WG call, direction on removing section 7.3.2 and consolidating its content in Nonce Endpoint definition. https://openid.github.io/OpenID4VCI/openid-4-verifiable-credential-issuance-wg-draft.html#section-7.3.2

While I was part of that discussion, after looking again at that section and content of this PR, I don't see how that consolation could actually manifest in a meaningful way. I suggest this PR proceed without and consider that as part of the soon to be separate issue on removing an option to return c_nonce from the credential [error] response.

also agreed to open a separate issue on removing an option to return c_nonce from the credential error response, so that we can merge this PR as-is (@bc-pi).

that is this

[bc-pi]

I guess there's the potential to consider two different things here: 1) c_nonce in a credential error response and 2) c_nonce in a successful credential response.

But I'm mostly of the mind to treat it as all or nothing.

[bc-pi]

when/if/after ...

[mickrau]

I am in favor of removing the c_nonce option from credential response completely. I don't see any advantage from this optional feature that justifies the extra effort on the wallet side.

In my opinion, there should only be one way to get a nonce.