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/bookctrl.h

@@ -179,11 +179,6 @@ public:
         }
     }
 
-    // override some base class virtuals
-    virtual void ApplyParentThemeBackground(const wxColour& bg)
-        { SetBackgroundColour(bg); }
-    virtual bool ProvidesBackground() const { return true; }
-
 protected:
     // remove the page and return a pointer to it
     virtual wxWindow *DoRemovePage(size_t page) = 0;