Plane: remove pointless rangefinder_init shim function

ArduPlane/Plane.h

@@ -912,7 +912,6 @@ private:
     void control_failsafe();
     bool trim_radio();
     bool rc_failsafe_active(void);
-    void init_rangefinder(void);
     void read_rangefinder(void);
     void read_airspeed(void);
     void rpm_update(void);

ArduPlane/sensors.cpp

@@ -1,11 +1,6 @@
 #include "Plane.h"
 #include <AP_RSSI/AP_RSSI.h>
 
-void Plane::init_rangefinder(void)
-{
-    rangefinder.init();
-}
-
 /*
   read the rangefinder and update height estimate
  */

ArduPlane/system.cpp

@@ -103,7 +103,7 @@ void Plane::init_ardupilot()
     barometer.init();
 
     // initialise rangefinder
-    init_rangefinder();
+    rangefinder.init();
 
     // initialise battery monitoring
     battery.init();