vehicle_local_position: delete unused and redundant dist_bottom_rate

msg/vehicle_local_position.msg

@@ -49,7 +49,6 @@ float32 ref_alt				# Reference altitude AMSL, (metres)
 
 # Distance to surface
 float32 dist_bottom			# Distance from from bottom surface to ground, (metres)
-float32 dist_bottom_rate		# Rate of change of distance from bottom surface to ground, (metres/sec)
 bool dist_bottom_valid			# true if distance to bottom surface is valid
 
 float32 eph				# Standard deviation of horizontal position error, (metres)

src/modules/ekf2/ekf2_main.cpp

@@ -1327,8 +1327,6 @@ void Ekf2::Run()
 					_ekf.set_gnd_effect_flag(false);
 				}
 
-				lpos.dist_bottom_rate = -lpos.vz; // Distance to bottom surface (ground) change rate
-
 				_ekf.get_ekf_lpos_accuracy(&lpos.eph, &lpos.epv);
 				_ekf.get_ekf_vel_accuracy(&lpos.evh, &lpos.evv);
 

src/modules/local_position_estimator/BlockLocalPositionEstimator.cpp

@@ -604,7 +604,6 @@ void BlockLocalPositionEstimator::publishLocalPos()
 		_pub_lpos.get().ref_lon = _map_ref.lon_rad * 180 / M_PI;
 		_pub_lpos.get().ref_alt = _altOrigin;
 		_pub_lpos.get().dist_bottom = _aglLowPass.getState();
-		_pub_lpos.get().dist_bottom_rate = -xLP(X_vz);
 		// we estimate agl even when we don't have terrain info
 		// if you are in terrain following mode this is important
 		// so that if terrain estimation fails there isn't a