Disconnect handshake message creation from init_buf.

This allows us to use CBB for all handshake messages. Now, SSL_PROTOCOL_METHOD
is responsible for implementing a trio of CBB-related hooks to assemble
handshake messages.

Change-Id: I144d3cac4f05b6637bf45d3f838673fc5c854405
Reviewed-on: https://boringssl-review.googlesource.com/8440
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/d1_meth.c b/ssl/d1_meth.c
index 32a4651..78119a0 100644
--- a/ssl/d1_meth.c
+++ b/ssl/d1_meth.c
@@ -70,9 +70,9 @@
     dtls1_write_app_data,
     dtls1_dispatch_alert,
     dtls1_supports_cipher,
-    DTLS1_HM_HEADER_LENGTH,
-    dtls1_set_handshake_header,
-    dtls1_handshake_write,
+    dtls1_init_message,
+    dtls1_finish_message,
+    dtls1_write_message,
     dtls1_send_change_cipher_spec,
     dtls1_expect_flight,
     dtls1_received_flight,