Remove horizontal slow down close to ground

Because based on the numerous complaints it was disabled by default
(only velocities above 10m/s were limited)
and since then no one intentionally used it anymore. But
there were some minor investigations of drones not reaching
their maximum speed which always showed 10m/s.

src/modules/flight_mode_manager/tasks/ManualPosition/FlightTaskManualPosition.cpp

@@ -102,8 +102,6 @@ void FlightTaskManualPosition::_scaleSticks()
 		_velocity_scale = _constraints.speed_xy;
 	}
 
-	_velocity_scale = fminf(_computeVelXYGroundDist(), _velocity_scale);
-
 	// scale velocity to its maximum limits
 	Vector2f vel_sp_xy = stick_xy * _velocity_scale;
 
@@ -118,20 +116,6 @@ void FlightTaskManualPosition::_scaleSticks()
 	_velocity_setpoint.xy() = vel_sp_xy;
 }
 
-float FlightTaskManualPosition::_computeVelXYGroundDist()
-{
-	float max_vel_xy = _constraints.speed_xy;
-
-	// limit speed gradually within the altitudes MPC_LAND_ALT1 and MPC_LAND_ALT2
-	if (PX4_ISFINITE(_dist_to_ground)) {
-		max_vel_xy = math::gradual(_dist_to_ground,
-					   _param_mpc_land_alt2.get(), _param_mpc_land_alt1.get(),
-					   _param_mpc_land_vel_xy.get(), _constraints.speed_xy);
-	}
-
-	return max_vel_xy;
-}
-
 void FlightTaskManualPosition::_updateXYlock()
 {
 	/* If position lock is not active, position setpoint is set to NAN.*/

src/modules/flight_mode_manager/tasks/ManualPosition/FlightTaskManualPosition.hpp

@@ -65,12 +65,10 @@ protected:
 
 	DEFINE_PARAMETERS_CUSTOM_PARENT(FlightTaskManualAltitude,
 					(ParamFloat<px4::params::MPC_VEL_MANUAL>) _param_mpc_vel_manual,
-					(ParamFloat<px4::params::MPC_LAND_VEL_XY>) _param_mpc_land_vel_xy,
 					(ParamFloat<px4::params::MPC_ACC_HOR_MAX>) _param_mpc_acc_hor_max,
 					(ParamFloat<px4::params::MPC_HOLD_MAX_XY>) _param_mpc_hold_max_xy
 				       )
 private:
-	float _computeVelXYGroundDist();
 	float _velocity_scale{0.0f}; //scales the stick input to velocity
 	uint8_t _reset_counter{0}; /**< counter for estimator resets in xy-direction */