Clean up wxDropTarget and wxWindow a bit more by moving DnD stuff fully into drop target (besides connecting and disconnecting).

Window doesn't have to know more than how to hook itself up.
Impl now performs function of event filter/adapter.

include/wx/qt/window.h

@@ -217,16 +217,6 @@ protected:
     QWidget *m_qtWindow;
 
 private:
-    class DnDEventAdapter : public QObject
-    {
-    public:
-        DnDEventAdapter();
-        virtual bool eventFilter(QObject* watched, QEvent* event);
-        void SetDropTarget(wxDropTarget* dropTarget, QWidget* window);
-    private:
-        wxDropTarget *m_dropTarget;
-    };
-
     void Init();
     QScrollArea *m_qtContainer;
 
@@ -249,10 +239,6 @@ private:
     bool m_processingShortcut;
 #endif // wxUSE_ACCEL
 
-#if wxUSE_DRAG_AND_DROP
-    DnDEventAdapter dnd_event_adapter;
-#endif
-
     wxDECLARE_DYNAMIC_CLASS_NO_COPY( wxWindowQt );
 };