Remove unused field

Fixes #1775 <https://github.com/Genymobile/scrcpy/issues/1775>

Reported-by: lordnn

app/src/stream.h

@@ -14,7 +14,6 @@ struct video_buffer;
 
 struct stream {
     socket_t socket;
-    struct video_buffer *video_buffer;
     SDL_Thread *thread;
     struct decoder *decoder;
     struct recorder *recorder;