Removed unused code pertaining to shared_ptr

python/google/protobuf/pyext/message.h

@@ -52,13 +52,6 @@ class Descriptor;
 class DescriptorPool;
 class MessageFactory;
 
-#ifdef _SHARED_PTR_H
-using std::shared_ptr;
-using std::string;
-#else
-using internal::shared_ptr;
-#endif
-
 namespace python {
 
 struct ExtensionDict;