Temporarily disable DwmFlush()

For some reason this locks up the Windows compositor when called by Steam. I'm disabling it for now until we understand why and whether this can cause issues for other applications as well.

(cherry picked from commit a23f97483f5a654eadc6b8e66fdf65038fc2d0d8)

src/video/windows/SDL_windowsevents.c

@@ -1861,10 +1861,12 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
             SDL_OnWindowLiveResizeUpdate(data->window);
 
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)
+#if 0 // This locks up the Windows compositor when called by Steam; disabling until we understand why
             // Make sure graphics operations are complete for smooth refresh
             if (data->videodata->DwmFlush) {
                 data->videodata->DwmFlush();
             }
+#endif
 #endif
             return 0;
         }