remove count_hydrogen_sites()

it was too specific, instead of it use
 has_hydrogen() -> bool
or
 Selection sel("[H,D]");
 count_atom_sites(..., sel);

include/gemmi/calculate.hpp

@@ -22,17 +22,6 @@ template<> inline bool has_hydrogen(const Atom& atom) {
   return atom.is_hydrogen();
 }
 
-/// deprecated, use has_hydrogen() or count_atom_sites(..., Selection("[H,D]")
-template<class T> size_t count_hydrogen_sites(const T& obj) {
-  size_t sum = 0;
-  for (const auto& child : obj.children())
-    sum += count_hydrogen_sites(child);
-  return sum;
-}
-template<> inline size_t count_hydrogen_sites(const Atom& atom) {
-  return (size_t) atom.is_hydrogen();
-}
-
 template<class T> size_t count_atom_sites(const T& obj, const Selection* sel=nullptr) {
   size_t sum = 0;
   if (!sel || sel->matches(obj))

python/mol.cpp

@@ -268,8 +268,6 @@ void add_mol(nb::module_& m) {
     .def("remove_ligands_and_waters", remove_ligands_and_waters<Model>)
     .def("has_hydrogen", &has_hydrogen<Model>)
     .def("count_atom_sites", &count_atom_sites<Model>, nb::arg("sel")=nb::none())
-    // deprecated, use has_hydrogen() or count_atom_sites(Selection('[H,D]'))
-    .def("count_hydrogen_sites", &count_hydrogen_sites<Model>)
     .def("count_occupancies", &count_occupancies<Model>, nb::arg("sel")=nb::none())
     .def("calculate_mass", &calculate_mass<Model>)
     .def("calculate_center_of_mass", [](const Model& self) {