Sub: Remove rangefinder support of control loops

The rangefinder handling doesn't handle sonar glitches like
locking on to reflections very well. We will remove the
rangefinder as an input to the controllers until we can do a
more robust implementation.

ArduSub/control_althold.cpp

@@ -112,10 +112,6 @@ void Sub::althold_run()
         if (ap.at_bottom) {
             pos_control.relax_alt_hold_controllers(); // clear velocity and position targets
             pos_control.set_alt_target(inertial_nav.get_altitude() + 10.0f); // set target to 10 cm above bottom
-        } else if (rangefinder_alt_ok()) {
-            // if rangefinder is ok, use surface tracking
-            float target_climb_rate = get_surface_tracking_climb_rate(0, pos_control.get_alt_target(), G_Dt);
-            pos_control.set_alt_target_from_climb_rate_ff(target_climb_rate, G_Dt, false);
         }
 
         // Detects a zero derivative

ArduSub/control_circle.cpp

@@ -82,11 +82,6 @@ void Sub::circle_run()
         attitude_control.input_euler_angle_roll_pitch_yaw(channel_roll->get_control_in(), channel_pitch->get_control_in(), circle_nav.get_yaw(), true);
     }
 
-    // adjust climb rate using rangefinder
-    if (rangefinder_alt_ok()) {
-        // if rangefinder is ok, use surface tracking
-        target_climb_rate = get_surface_tracking_climb_rate(target_climb_rate, pos_control.get_alt_target(), G_Dt);
-    }
     // update altitude target and call position controller
     pos_control.set_alt_target_from_climb_rate(target_climb_rate, G_Dt, false);
     pos_control.update_z_controller();

ArduSub/control_poshold.cpp

@@ -116,12 +116,6 @@ void Sub::poshold_run()
     float target_climb_rate = get_pilot_desired_climb_rate(channel_throttle->get_control_in());
     target_climb_rate = constrain_float(target_climb_rate, -get_pilot_speed_dn(), g.pilot_speed_up);
 
-    // adjust climb rate using rangefinder
-    if (rangefinder_alt_ok()) {
-        // if rangefinder is ok, use surface tracking
-        target_climb_rate = get_surface_tracking_climb_rate(target_climb_rate, pos_control.get_alt_target(), G_Dt);
-    }
-
     // call z axis position controller
     if (ap.at_bottom) {
         pos_control.relax_alt_hold_controllers(motors.get_throttle_hover()); // clear velocity and position targets, and integrator