DiabloUI: Always blit to `PalSurface`

Previously we were blitting to the output surface directly.

Blitting to `PalSurface` allows us to support CEL/CL2 rendering in the
main menu.

Source/DiabloUI/diabloui.h

@@ -78,18 +78,7 @@ extern bool (*gfnHeroInfo)(bool (*fninfofunc)(_uiheroinfo *));
 
 inline SDL_Surface *DiabloUiSurface()
 {
-	auto *output_surface = GetOutputSurface();
-
-#ifdef USE_SDL1
-	// When using a non double-buffered hardware surface, render the UI
-	// to an off-screen surface first to avoid flickering / tearing.
-	if ((output_surface->flags & SDL_HWSURFACE) != 0
-	    && (output_surface->flags & SDL_DOUBLEBUF) == 0) {
-		return PalSurface;
-	}
-#endif
-
-	return output_surface;
+	return PalSurface;
 }
 
 void UiDestroy();