Reject ECDSA Keys/Certificates With Explicitly Encoded Curve Parameters

[tobiasbrunner]

Discussed in #1796

There is a relatively recent NIAP requirement to reject certificates with ECDSA keys that explicitly encode the curve parameters (TD0527, Test 8b). Since explicit encoding is pretty rare (if used at all and e.g. wolfSSL already rejects it, by default), we should follow that requirement and just reject such keys/certificates completely.