code: use macros for default node functions

Easier to maintain

app/node/audio/volume/volume.cpp

@@ -41,11 +41,6 @@ VolumeNode::VolumeNode()
   SetEffectInput(kSamplesInput);
 }
 
-Node *VolumeNode::copy() const
-{
-  return new VolumeNode();
-}
-
 QString VolumeNode::Name() const
 {
   return tr("Volume");

app/node/audio/volume/volume.h

@@ -31,9 +31,7 @@ class VolumeNode : public MathNodeBase
 public:
   VolumeNode();
 
-  NODE_DEFAULT_DESTRUCTOR(VolumeNode)
-
-  virtual Node* copy() const override;
+  NODE_DEFAULT_FUNCTIONS(VolumeNode)
 
   virtual QString Name() const override;
   virtual QString id() const override;