Rename ssl_locl.h to internal.h

Match the other internal headers.

Change-Id: Iff7e2dd06a1a7bf993053d0464cc15638ace3aaa
Reviewed-on: https://boringssl-review.googlesource.com/4280
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 7826bf49..81e76c4 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -163,7 +163,7 @@
 #include <openssl/engine.h>
 #include <openssl/x509.h>
 
-#include "ssl_locl.h"
+#include "internal.h"
 #include "../crypto/dh/internal.h"