Plane: Remove unneeded GCS rally override

ArduPlane/GCS_Mavlink.cpp

@@ -1530,11 +1530,6 @@ AP_AdvancedFailsafe *GCS_MAVLINK_Plane::get_advanced_failsafe() const
     return &plane.afs;
 }
 
-AP_Rally *GCS_MAVLINK_Plane::get_rally() const
-{
-    return &plane.rally;
-}
-
 /*
   set_mode() wrapper for MAVLink SET_MODE
  */

ArduPlane/GCS_Mavlink.h

@@ -17,7 +17,6 @@ protected:
     void handle_mission_set_current(AP_Mission &mission, mavlink_message_t *msg) override;
 
     AP_AdvancedFailsafe *get_advanced_failsafe() const override;
-    AP_Rally *get_rally() const override;
 
     uint8_t sysid_my_gcs() const override;
     bool sysid_enforce() const override;