[openssl/openssl] 157c40: remove duplicate defines, add comment

[Pauli]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 157c40e4d0a2c901e2dc0ee29b80a079a548d008
      https://github.com/openssl/openssl/commit/157c40e4d0a2c901e2dc0ee29b80a079a548d008
  Author: Pauli <pauli at openssl.org>
  Date:   2023-07-19 (Wed, 19 Jul 2023)

  Changed paths:
    M include/internal/quic_types.h

  Log Message:
  -----------
  remove duplicate defines, add comment

Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
Reviewed-by: Tim Hudson <tjh at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21441)