message: Use simplices iterator instead of skeleton iterator
diff: @@ -1203,7 +1203,7 @@ class Simplex_tree {
  bool downgrade_dimension() {
  int new_dimension = -1;
  // Browse the tree from the left to the right as higher dimension cells are more likely on the left part of the tree
  - for (Simplex_handle sh : skeleton_simplex_range(dimension_)) {
  + for (Simplex_handle sh : complex_simplex_range()) {
  #ifdef DEBUG_TRACES
  for (auto vertex : simplex_vertex_range(sh)) {
  std::cout << " " << vertex;
  