Imprecise changelog items related to nonce endpoint

[matzf]

The document history contains small errors related to adding the nonce endpoint and removing c_nonce from token and credential endpoints:

The following entries in the -14 subsection of the document history refer to changes that were completed in draft version 15:

* removed c_nonce and c_nonce_expires_in from the token endpoint response
* added a Nonce Endpoint where a Client can acquire a fresh c_nonce value without the overhead of a full Credential Request

The following entry in the -15 subsection of the document history is inaccurate:

* removes `c_nonce` and `c_nonce_expires_in` from the Credential Error Response

The c_nonce fields were removed from the credential endpoint entirely, both for success and error responses.

[babisRoutis]

Indeed I have also noticed those small discrepancies.

For draft 14, I think the correct version is here

[Sakurann]

please review the PR