Rover: use camera singleton to get camera rather than callback

APMrover2/GCS_Mavlink.cpp

@@ -1268,15 +1268,6 @@ bool GCS_MAVLINK_Rover::accept_packet(const mavlink_status_t &status, mavlink_me
     return (msg.sysid == rover.g.sysid_my_gcs);
 }
 
-AP_Camera *GCS_MAVLINK_Rover::get_camera() const
-{
-#if CAMERA == ENABLED
-    return &rover.camera;
-#else
-    return nullptr;
-#endif
-}
-
 AP_AdvancedFailsafe *GCS_MAVLINK_Rover::get_advanced_failsafe() const
 {
 #if ADVANCED_FAILSAFE == ENABLED

APMrover2/GCS_Mavlink.h

@@ -16,7 +16,6 @@ protected:
 
     AP_Mission *get_mission() override;
     AP_Rally *get_rally() const override;
-    AP_Camera *get_camera() const override;
     AP_AdvancedFailsafe *get_advanced_failsafe() const override;
     AP_VisualOdom *get_visual_odom() const override;