Rover: use gps singleton for GCS functions

APMrover2/GCS_Mavlink.cpp

@@ -1391,11 +1391,6 @@ bool GCS_MAVLINK_Rover::accept_packet(const mavlink_status_t &status, mavlink_me
     return (msg.sysid == rover.g.sysid_my_gcs);
 }
 
-AP_GPS *GCS_MAVLINK_Rover::get_gps() const
-{
-    return &rover.gps;
-}
-
 AP_Camera *GCS_MAVLINK_Rover::get_camera() const
 {
 #if CAMERA == ENABLED

APMrover2/GCS_Mavlink.h

@@ -21,7 +21,6 @@ protected:
     AP_Rally *get_rally() const override { return nullptr; };
     AP_Camera *get_camera() const override;
     AP_ServoRelayEvents *get_servorelayevents() const override;
-    AP_GPS *get_gps() const override;
     AP_AdvancedFailsafe *get_advanced_failsafe() const override;
     const AP_FWVersion &get_fwver() const override;
     void set_ekf_origin(const Location& loc) override;