rtmp-common: Use "rate_control" to set CBR mode

Instead of using "cbr" to set the rate control mode for encoders (which
is now considered deprecated for all encoders), set "rate_control" to
"CBR".

plugins/rtmp-services/rtmp-common.c

@@ -329,7 +329,7 @@ static void apply_video_encoder_settings(obs_data_t *settings,
 		obs_data_set_int(settings, "keyint_sec", keyint);
 	}
 
-	obs_data_set_bool(settings, "cbr", true);
+	obs_data_set_string(settings, "rate_control", "CBR");
 
 	item = json_object_get(recommended, "profile");
 	if (item && json_is_string(item)) {