Remove copy-assigns.

src/ngraph/element_type.hpp

@@ -31,6 +31,7 @@ namespace ngraph
         class Type
         {
             Type(const Type&) = delete;
+            Type& operator=(const Type&) = delete;
         public:
             Type(size_t bitwidth, bool is_float, bool is_signed, const std::string& cname);
 
@@ -77,6 +78,7 @@ namespace ngraph
         class TraitedType : public Type
         {
             TraitedType(const TraitedType&) = delete;
+            TraitedType& operator=(const TraitedType&) = delete;
         protected:
             TraitedType()
                 : Type(sizeof(T) * 8,