The method is removed because it does not really help with
anything. It should not be exported from wined3d, there is no need for
the other libs to call it. It does not help abstraction and code
simplification in any way because it is very specific and the code
calling it has to know what is happening in the surface to use this
method.
OpenGL AUX buffers provide a way for offscreen rendering which is very
similar to our back buffer "offscreen" rendering emulation. Not all
card support aux buffers, but if they are available they are a nice
present which is easy to use.