commander: take main_state out of vehicle_status

This state is only commander internal. Therefore it doesn't need to be
in vehicle_status. Instead it is now in the commander_state message.

src/modules/uORB/objects_common.cpp

@@ -288,3 +288,6 @@ ORB_DEFINE(mavlink_log, struct mavlink_log_s);
 
 #include "topics/follow_target.h"
 ORB_DEFINE(follow_target, struct follow_target_s);
+
+#include "topics/commander_state.h"
+ORB_DEFINE(commander_state, struct commander_state_s);