AC_AttitudeControl: remove unused get_tilt_limit_rad

libraries/AC_AttitudeControl/AC_AttitudeControl.h

@@ -303,9 +303,6 @@ protected:
     // Return the yaw slew rate limit in radians/s
     float get_slew_yaw_rads() { return radians(_slew_yaw*0.01f); }
 
-    // Return the tilt angle limit in radians
-    float get_tilt_limit_rad() { return radians(_aparm.angle_max*0.01f); }
-
     // Maximum rate the yaw target can be updated in Loiter, RTL, Auto flight modes
     AP_Float            _slew_yaw;