Removes unused property use_egl from internal structure gl_config

src/video/SDL_sysvideo.h

@@ -292,7 +292,6 @@ struct SDL_VideoDevice
         int minor_version;
         int flags;
         int profile_mask;
-        int use_egl;
         int share_with_current_context;
         int retained_backing;
         int driver_loaded;