simplifications and corrections to background drawing:

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