delete SYS_MC_EST_GROUP

- introduce per module parameters (EKF2_EN, LPE_EN, ATT_EN)
 - add basic checks to prevent EKF2 + LPE running simultaneously

src/modules/ekf2/EKF2.cpp

@@ -237,7 +237,6 @@ EKF2::~EKF2()
 bool EKF2::multi_init(int imu, int mag)
 {
 	// advertise all topics to ensure consistent uORB instance numbering
-	_ekf2_timestamps_pub.advertise();
 	_estimator_event_flags_pub.advertise();
 	_estimator_innovation_test_ratios_pub.advertise();
 	_estimator_innovation_variances_pub.advertise();