Remove default bit-rate on client side

If no bit-rate is passed, let the server use the default value (8Mbps).

This avoids to define a default value on both sides, and to pass the
default bit-rate as an argument when starting the server.

app/src/options.c

@@ -27,7 +27,7 @@ const struct scrcpy_options scrcpy_options_default = {
         .count = 2,
     },
     .max_size = 0,
-    .bit_rate = DEFAULT_BIT_RATE,
+    .bit_rate = 0,
     .max_fps = 0,
     .lock_video_orientation = SC_LOCK_VIDEO_ORIENTATION_UNLOCKED,
     .rotation = 0,