Update delegated credentials to the final RFC

Although the comments say draft-03, we're currently on draft-06.
dcd6e447eba4f32f49c22c6196ed0e714cc522c1 forgot to update all the
comments.

The final RFC is identical to draft-06, except
expected_cert_verify_algorithm was renamed to dc_cert_verify_algorithm,
so this is just changing comment and renaming something.

While I'm here, write the codepoint in decimal instead of hex, to match
the document and how the other IANA codepoints are written out.

Change-Id: I6d1f362a21eecafeef5bba5879f4158e31c8def4
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/66367
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Auto-Submit: David Benjamin <davidben@google.com>