Remove default copyop argument for nodecallback copy constructors

Works around a compiler warning with OSG 3.4:

warning: base class 'class osg::Callback' should be explicitly initialized in the copy constructor [-Wextra]

With no default argument for osg::CopyOp&, the compiler no longer sees the function as a real copy constructor and stops warning about the missing virtual initializations.

We don't care about this warning because there is nothing interesting to initialize in the osg::NodeCallback base anyway.

A proper fix for the warning would require to inserting OSG_VERSION conditional compiling all over the place, that is as long as we are still supporting OSG 3.2.

components/nifosg/controller.hpp

@@ -146,7 +146,7 @@ namespace NifOsg
     {
     public:
         UVController();
-        UVController(const UVController&,const osg::CopyOp& = osg::CopyOp::SHALLOW_COPY);
+        UVController(const UVController&,const osg::CopyOp&);
         UVController(const Nif::NiUVData *data, std::set<int> textureUnits);
 
         META_Object(NifOsg,UVController)

components/nifosg/particle.hpp

@@ -60,7 +60,7 @@ namespace NifOsg
         InverseWorldMatrix()
         {
         }
-        InverseWorldMatrix(const InverseWorldMatrix& copy, const osg::CopyOp& op = osg::CopyOp::SHALLOW_COPY)
+        InverseWorldMatrix(const InverseWorldMatrix& copy, const osg::CopyOp& op)
             : osg::Object(), osg::NodeCallback()
         {
         }

components/sceneutil/lightmanager.hpp

@@ -121,7 +121,7 @@ namespace SceneUtil
             : mLightManager(NULL)
             , mLastFrameNumber(0)
         {}
-        LightListCallback(const LightListCallback& copy, const osg::CopyOp& copyop = osg::CopyOp::SHALLOW_COPY)
+        LightListCallback(const LightListCallback& copy, const osg::CopyOp& copyop)
             : osg::Object(copy, copyop), osg::NodeCallback(copy, copyop)
             , mLightManager(copy.mLightManager)
             , mLastFrameNumber(0)