Pass video size as codec metadata

On initial connection, scrcpy sent some device metadata:
 - the device name (to be used as window title)
 - the initial video size (before any frame or even SPS/PPS)

But it is better to provide the initial video size as part as the video
stream, so that it can be demuxed and exposed via AVCodecContext to
sinks.

This avoids to pass an explicit "initial frame size" for the screen, the
recorder and the v4l2 sink.

app/src/screen.h

@@ -78,7 +78,6 @@ struct sc_screen_params {
     const struct sc_shortcut_mods *shortcut_mods;
 
     const char *window_title;
-    struct sc_size frame_size;
     bool always_on_top;
 
     int16_t window_x; // accepts SC_WINDOW_POSITION_UNDEFINED