Convert the Channel ID extension to the new system.

This also removes support for the “old” Channel ID extension.

Change-Id: I1168efb9365c274db6b9d7e32013336e4404ff54
Reviewed-on: https://boringssl-review.googlesource.com/5462
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 229a315..58f92ce 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -430,11 +430,9 @@
            * record the handshake hashes at this point in the session so that
            * any resumption of this session with ChannelID can sign those
            * hashes. */
-          if (s->s3->tlsext_channel_id_new) {
-            ret = tls1_record_handshake_hashes_for_channel_id(s);
-            if (ret <= 0) {
-              goto end;
-            }
+          ret = tls1_record_handshake_hashes_for_channel_id(s);
+          if (ret <= 0) {
+            goto end;
           }
           if ((SSL_get_mode(s) & SSL_MODE_ENABLE_FALSE_START) &&
               ssl3_can_false_start(s) &&
@@ -2196,11 +2194,7 @@
   EC_KEY *ec_key = s->tlsext_channel_id_private->pkey.ec;
 
   d = ssl_handshake_start(s);
-  if (s->s3->tlsext_channel_id_new) {
-    s2n(TLSEXT_TYPE_channel_id_new, d);
-  } else {
-    s2n(TLSEXT_TYPE_channel_id, d);
-  }
+  s2n(TLSEXT_TYPE_channel_id, d);
   s2n(TLSEXT_CHANNEL_ID_SIZE, d);
 
   EVP_MD_CTX_init(&md_ctx);