Plane: use gps singleton for GCS functions

ArduPlane/GCS_Mavlink.cpp

@@ -1930,11 +1930,6 @@ void GCS_MAVLINK_Plane::handle_mission_set_current(AP_Mission &mission, mavlink_
     }
 }
 
-AP_GPS *GCS_MAVLINK_Plane::get_gps() const
-{
-    return &plane.gps;
-}
-
 AP_Camera *GCS_MAVLINK_Plane::get_camera() const
 {
 #if CAMERA == ENABLED

ArduPlane/GCS_Mavlink.h

@@ -26,7 +26,6 @@ protected:
     AP_ServoRelayEvents *get_servorelayevents() const override;
     AP_AdvancedFailsafe *get_advanced_failsafe() const override;
     AP_Rally *get_rally() const override;
-    AP_GPS *get_gps() const override;
     const AP_FWVersion &get_fwver() const override;
     void set_ekf_origin(const Location& loc) override;