ArduPlane: remove unused update_transition() definition

ArduPlane/quadplane.cpp

@@ -2366,7 +2366,7 @@ void QuadPlane::vtol_position_controller(void)
 
     case QPOS_APPROACH:
         if (in_vtol_mode()) {
-            // this means we're not running update_transition() and
+            // this means we're not running transition update code and
             // thus not doing qassist checking, force POSITION1 mode
             // now. We don't expect this to trigger, it is a failsafe
             // for a logic error

ArduPlane/quadplane.h

@@ -223,9 +223,6 @@ private:
     // check for quadplane assistance needed
     bool should_assist(float aspeed, bool have_airspeed);
 
-    // update transition handling
-    void update_transition(void);
-
     // check for an EKF yaw reset
     void check_yaw_reset(void);