Fix drag move of wxMiniFrame under Wayland

Use gtk_window_begin_move_drag() instead of trying to do it manually
See #18372

include/wx/gtk/minifram.h

@@ -52,9 +52,6 @@ protected:
 
  // implementation
 public:
-    bool   m_isDragging;
-    int    m_oldX,m_oldY;
-    int    m_diffX,m_diffY;
     wxBitmap  m_closeButton;
     int m_miniEdge;
     int m_miniTitle;