Remove rank/select storage to file in Coverind

rank_support and select_support are constant space classes that do not
store anything. It is useless to try to store them

coverind.hpp

@@ -173,10 +173,6 @@ template <class bv>
 void Coverind<bv>::save(const std::string filename) const {
   store_to_file(start, filename + std::string(".start.bv"));
   store_to_file(end, filename + std::string(".end.bv"));
-  store_to_file(rank_start, filename + std::string(".start.rank"));
-  store_to_file(rank_end, filename + std::string(".end.rank"));
-  store_to_file(select_start, filename + std::string(".start.select"));
-  store_to_file(select_end, filename + std::string(".end.select"));
 }
 
 bit_vector create_bitvector_from_file(const std::string filename) {