remove virtual

paddle/framework/net.h

@@ -91,8 +91,6 @@ class Net {
    * @brief Create a network.
    */
   static std::unique_ptr<Net> Create(const NetDesc &def = NetDesc());
-
-  virtual ~Net() = 0;
 };
 
 /**
@@ -142,8 +140,6 @@ class PlainNet : public Net {
    */
   virtual void AddBackwardOps() override;
 
-  virtual ~PlainNet() override {}
-
  protected:
   /**
    * @brief Build the network.