Revert scoped_types.h change.

This reverts commits:
8d79ed67407e433d80ebc8d3aa080e8ce16e6eb7
19fdcb523402ed13ab798cf811fb0119e3e7b104
8d79ed67407e433d80ebc8d3aa080e8ce16e6eb7

Because WebRTC (at least) includes our headers in an extern "C" block,
which precludes having any C++ in them.

Change-Id: Ia849f43795a40034cbd45b22ea680b51aab28b2d
diff --git a/crypto/bn/bn_test.cc b/crypto/bn/bn_test.cc
index 67ab924..3028745 100644
--- a/crypto/bn/bn_test.cc
+++ b/crypto/bn/bn_test.cc
@@ -81,12 +81,12 @@
 #include <utility>
 
 #include <openssl/bn.h>
-#include <openssl/bytestring.h>
 #include <openssl/crypto.h>
 #include <openssl/err.h>
 #include <openssl/mem.h>
 
 #include "../crypto/test/file_test.h"
+#include "../crypto/test/scoped_types.h"
 #include "../crypto/test/test_util.h"