moved ProvidesBackground() from wxUniv to base wxWindow class; use it to prevent inheriting background brush beyond the windows which normally have their own background

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31073 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/univ/toplevel.h

@@ -143,8 +143,6 @@ public:
     virtual int GetMinWidth() const;
     virtual int GetMinHeight() const;
 
-    virtual bool ProvidesBackground() const { return true; }
-    
 protected:
     // handle titlebar button click event
     virtual void ClickTitleBarButton(long button);