Ax ScaleSurfaceSlow() in favor of ScaleSurface()

ScaleSurfaceSlow() uses DrawPixel() instead of SDL_FillRect() to scale a
given surface, which is slow and inefficient, and makes it less likely
that the game could be moved to SDL_Render.

Unfortunately, it has this weird -1,-1 offset, but that will be fixed in
the next commit.

desktop_version/src/GraphicsUtil.h

@@ -43,7 +43,6 @@ void ScrollSurface(SDL_Surface* _src, int pX, int py);
 
 SDL_Surface * FlipSurfaceHorizontal(SDL_Surface* _src);
 SDL_Surface * FlipSurfaceVerticle(SDL_Surface* _src);
-SDL_Surface * ScaleSurfaceSlow( SDL_Surface *_surface, int Width, int Height );
 void UpdateFilter();
 SDL_Surface* ApplyFilter( SDL_Surface* _src );