Do not set num_threads to 1 (#565)

This fixes an error introduced in
8f05442
(cf. #555)

Author: vil02

include/CXXGraph/Graph/Algorithm/BestFirstSearch_impl.hpp

@@ -112,7 +112,6 @@ BestFirstSearchResult<T> Graph<T>::best_first_search(
 template <typename T>
 const std::vector<Node<T>> Graph<T>::concurrency_breadth_first_search(
     const Node<T> &start, size_t num_threads) const {
-  num_threads = 1;
   std::vector<Node<T>> bfs_result;
   // check is exist node in the graph
   auto &nodeSet = Graph<T>::getNodeSet();