Removed osgGA::GUIEventHandlerVisitor and osgGA::SetSceneVistor classes/headers as

this classes weren't being actively used the distribution, effectively being noops.

src/osgGA/GUIEventHandler.cpp

@@ -49,52 +49,3 @@ void GUIEventHandler::event(osg::NodeVisitor* nv, osg::Drawable* drawable)
     }
 }
 
-void CompositeGUIEventHandler::getUsage(osg::ApplicationUsage& usage) const
-{
-    for (ChildList::const_iterator itr=_children.begin();
-        itr!=_children.end();
-        ++itr)
-    {
-        (*itr)->getUsage(usage);
-    }
-}
-
-bool CompositeGUIEventHandler::handle(const GUIEventAdapter& ea,GUIActionAdapter& aa, osg::Object* object, osg::NodeVisitor* nv)
-{
-    bool result=false;
-
-    for (ChildList::iterator itr=_children.begin();
-         itr!=_children.end();
-         ++itr)
-    {
-        result |= (*itr)->handle(ea, aa, object, nv);
-    }
-    return result;
-}
-
-
-bool CompositeGUIEventHandler::addChild(GUIEventHandler *child)
-{
-    if (child && !containsNode(child))
-    {
-        // note ref_ptr<> automatically handles incrementing child's reference count.
-        _children.push_back(child);
-        return true;
-    }
-    else return false;
-
-}
-
-bool CompositeGUIEventHandler::removeChild(GUIEventHandler *child)
-{
-    ChildList::iterator itr = findChild(child);
-    if (itr!=_children.end())
-    {
-        // note ref_ptr<> automatically handles decrementing child's reference count.
-        _children.erase(itr);
-
-        return true;
-    }
-    else return false;
-
-}