remove useless code

x2paddle/decoder/onnx_decoder.py

@@ -251,12 +251,7 @@ class ONNXGraph(Graph):
         """
         generate output_nodes node of ONNX model
         """
-        output_nodes = [value.name for value in self.graph.output]
-        for opt_data in output_nodes:
-            #n = super(ONNXGraph, self).get_node(opt_data)
-            #if n is None:
-            #    self.topo_sort.append(self.node_map[opt_data])
-            self.output_nodes.append(opt_data)
+        self.output_nodes = [value.name for value in self.graph.output]
 
     def is_place_holder_nodes(self, layer):
         """