simplifications and corrections to background drawing:

1. removed ApplyParentThemeBackground() not used any longer
2. removed ProvidesBackground() which is synonymous with
   !HasTransparentBackground()
3. removed a whole bunch of unused MSWXXX() methods
4. moved MSWControlColor() from wxWindow up to wxControl

results:

1. the gradient is still shown properly for static/radio boxes in notebooks
2. correct background colour is used for the static boxes
3. code is shorter and better commented


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@33474 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/checkbox.h

@@ -50,7 +50,6 @@ public:
 
 protected:
     virtual wxSize DoGetBestSize() const;
-    virtual WXHBRUSH MSWGetDefaultBgBrush();
 
     virtual void DoSet3StateValue(wxCheckBoxState value);
     virtual wxCheckBoxState DoGet3StateValue() const;