land_detector: Remove recently added vehicle_attitude.timestamp check from MulticopterLandDetector::_get_maybe_landed_state(). (#13072)

PR #12681 added a check to the MulticopterLandDetector::_get_maybe_landed_state() method for a valid vehicle_attitude.timstamp value to finish work in PR #9756. It was discovered that the addition of that check leaves it possible to fly in acro mode without a valid attitude and auto-disarm can engage, allowing the multicopter to fall out of the sky.

src/modules/land_detector/MulticopterLandDetector.cpp

@@ -178,7 +178,7 @@ bool MulticopterLandDetector::_get_maybe_landed_state()
 	const hrt_abstime now = hrt_absolute_time();
 
 	// When not armed, consider to be maybe-landed
-	if (!_actuator_armed.armed || (_vehicle_attitude.timestamp == 0)) {
+	if (!_actuator_armed.armed) {
 		return true;
 	}