Remove unused typedef error_info_str
diff --git a/ndn-cpp/common.h b/ndn-cpp/common.h
index 2acfd47..99e8fae 100644
--- a/ndn-cpp/common.h
+++ b/ndn-cpp/common.h
@@ -116,9 +116,5 @@
   else
     return BytesPtr ();
 }
-
-// Exceptions
-typedef boost::error_info<struct tag_errmsg, std::string> error_info_str;
-
 } // ndn
 #endif // NDN_COMMON_H