Plane: remove old commented code

- leftover from the AP_Landing stage refactor

ArduPlane/ArduPlane.cpp

@@ -943,21 +943,7 @@ void Plane::update_flight_stage(void)
                 } else {
                     set_flight_stage(AP_Vehicle::FixedWing::FLIGHT_LAND);
                 }
-/*
-   // FIXME: lift this into AP_Landing_Slope
-                } else if (flight_stage != AP_Vehicle::FixedWing::FLIGHT_LAND_APPROACH) {
-                    bool heading_lined_up = abs(nav_controller->bearing_error_cd()) < 1000 && !nav_controller->data_is_stale();
-                    const bool on_flight_line = fabsf(nav_controller->crosstrack_error()) < 5.0f && !nav_controller->data_is_stale();
-                    bool below_prev_WP = current_loc.alt < prev_WP_loc.alt;
-                    if ((mission.get_prev_nav_cmd_id() == MAV_CMD_NAV_LOITER_TO_ALT) ||
-                        (auto_state.wp_proportion >= 0 && heading_lined_up && on_flight_line) ||
-                        (auto_state.wp_proportion > 0.15f && heading_lined_up && below_prev_WP) ||
-                        (auto_state.wp_proportion > 0.5f)) {
-                        set_flight_stage(AP_Vehicle::FixedWing::FLIGHT_LAND_APPROACH);
-                    } else {
-                        set_flight_stage(AP_Vehicle::FixedWing::FLIGHT_NORMAL);
-                    }
-                }*/
+
             } else if (quadplane.in_assisted_flight()) {
                 set_flight_stage(AP_Vehicle::FixedWing::FLIGHT_VTOL);
             } else {