position controller main: Less verbose

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -857,10 +857,8 @@ MulticopterPositionControl::control_auto(float dt)
 void
 MulticopterPositionControl::task_main()
 {
-	warnx("started");
 
 	_mavlink_fd = open(MAVLINK_LOG_DEVICE, 0);
-	mavlink_log_info(_mavlink_fd, "[mpc] started");
 
 	/*
 	 * do subscriptions