message: backend: remove unused capture
diff: @@ -281,7 +281,7 @@ private:
  std::promise<void> mission_finished_promise;
  auto mission_finished_future = mission_finished_promise.get_future();
  - _mission.subscribe_progress([&writer, &mission_finished_promise](int current, int total) {
  + _mission.subscribe_progress([&writer](int current, int total) {
  dronecode_sdk::rpc::mission::MissionProgressResponse rpc_mission_progress_response;
  rpc_mission_progress_response.set_current_item_index(current);
  rpc_mission_progress_response.set_mission_count(total);
  