remove wxWindow::Clear() from wxDFB and wxMGL which was unused (probably replaced by ClearBackground()) and conflicted with methods with the same name in other classes

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49202 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/mgl/window.h

@@ -68,7 +68,6 @@ public:
     virtual void Refresh(bool eraseBackground = true,
                          const wxRect *rect = (const wxRect *) NULL);
     virtual void Update();
-    virtual void Clear();
     virtual void Freeze();
     virtual void Thaw();