fix link error for multiply-defined function (#3076)

test/pattern.cpp

@@ -292,17 +292,6 @@ TEST(pattern, graph_rewrite)
     }
 }
 
-std::ostream& operator<<(std::ostream& os, const ngraph::NodeVector& nv)
-{
-    std::vector<std::string> names;
-    for (auto n : nv)
-    {
-        names.push_back(n->get_name());
-    }
-    os << vector_to_string(names);
-    return os;
-}
-
 TEST(pattern, matcher)
 {
     Shape shape{};