Mavlink set last sent timestamp to space out initial publication

- remove QURT defines no longer required

src/modules/mavlink/mavlink_command_sender.cpp

@@ -57,15 +57,9 @@ void MavlinkCommandSender::initialize()
 
 MavlinkCommandSender &MavlinkCommandSender::instance()
 {
-
 	return *_instance;
 }
 
-MavlinkCommandSender::MavlinkCommandSender() :
-	_commands(3)
-{
-}
-
 MavlinkCommandSender::~MavlinkCommandSender()
 {
 	px4_sem_destroy(&_lock);