Rename ssl_set_handshake_header2()

ssl_set_handshake_header2() was only ever a temporary name while we had
to have ssl_set_handshake_header() for code that hadn't been converted to
WPACKET yet. No code remains that needed that so we can rename it.

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/ssl/d1_lib.c b/ssl/d1_lib.c
index 27b8ccb..112c699 100644
--- a/ssl/d1_lib.c
+++ b/ssl/d1_lib.c
@@ -42,7 +42,7 @@
     tls1_export_keying_material,
     SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV,
     DTLS1_HM_HEADER_LENGTH,
-    dtls1_set_handshake_header2,
+    dtls1_set_handshake_header,
     dtls1_close_construct_packet,
     dtls1_handshake_write
 };
@@ -62,7 +62,7 @@
     SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV | SSL_ENC_FLAG_SIGALGS
         | SSL_ENC_FLAG_SHA256_PRF | SSL_ENC_FLAG_TLS1_2_CIPHERS,
     DTLS1_HM_HEADER_LENGTH,
-    dtls1_set_handshake_header2,
+    dtls1_set_handshake_header,
     dtls1_close_construct_packet,
     dtls1_handshake_write
 };