navigator: remove dependency on vtol module by using the C param API

This is the quickest way to achieve the desired result.
Long-term we might do something else.

src/modules/navigator/navigator.h

@@ -283,8 +283,8 @@ public:
 	float		get_yaw_timeout() const { return _param_yaw_timeout.get(); }
 	float		get_yaw_threshold() const { return _param_yaw_err.get(); }
 
-	float		get_vtol_back_trans_deceleration() const { return _param_back_trans_dec_mss.get(); }
-	float		get_vtol_reverse_delay() const { return _param_reverse_delay.get(); }
+	float		get_vtol_back_trans_deceleration() const { return _param_back_trans_dec_mss; }
+	float		get_vtol_reverse_delay() const { return _param_reverse_delay; }
 
 	bool		force_vtol();
 
@@ -371,13 +371,14 @@ private:
 		(ParamFloat<px4::params::MIS_LTRMIN_ALT>) _param_loiter_min_alt,
 		(ParamFloat<px4::params::MIS_TAKEOFF_ALT>) _param_takeoff_min_alt,
 		(ParamFloat<px4::params::MIS_YAW_TMT>) _param_yaw_timeout,
-		(ParamFloat<px4::params::MIS_YAW_ERR>) _param_yaw_err,
-
-		// VTOL parameters TODO: get these out of navigator
-		(ParamFloat<px4::params::VT_B_DEC_MSS>) _param_back_trans_dec_mss,
-		(ParamFloat<px4::params::VT_B_REV_DEL>) _param_reverse_delay
+		(ParamFloat<px4::params::MIS_YAW_ERR>) _param_yaw_err
 	)
 
+	param_t _handle_back_trans_dec_mss{PARAM_INVALID};
+	param_t _handle_reverse_delay{PARAM_INVALID};
+	float _param_back_trans_dec_mss{0.f};
+	float _param_reverse_delay{0.f};
+
 	float _mission_cruising_speed_mc{-1.0f};
 	float _mission_cruising_speed_fw{-1.0f};
 	float _mission_throttle{-1.0f};

src/modules/navigator/navigator_main.cpp

@@ -110,6 +110,9 @@ Navigator::Navigator() :
 	_navigation_mode_array[8] = &_land;
 	_navigation_mode_array[9] = &_precland;
 	_navigation_mode_array[10] = &_follow_target;
+
+	_handle_back_trans_dec_mss = param_find("VT_B_DEC_MSS");
+	_handle_reverse_delay = param_find("VT_B_REV_DEL");
 }
 
 void
@@ -162,6 +165,14 @@ Navigator::params_update()
 	parameter_update_s param_update;
 	orb_copy(ORB_ID(parameter_update), _param_update_sub, &param_update);
 	updateParams();
+
+	if (_handle_back_trans_dec_mss != PARAM_INVALID) {
+		param_get(_handle_back_trans_dec_mss, &_param_back_trans_dec_mss);
+	}
+
+	if (_handle_reverse_delay != PARAM_INVALID) {
+		param_get(_handle_reverse_delay, &_param_reverse_delay);
+	}
 }
 
 void