message: remove unused template parameter in generate_fn::operator()
diff: @@ -44,7 +44,7 @@ namespace ranges
  return {detail::move(begin), detail::move(fun)};
  }
  - template<typename Rng, typename F, typename O = iterator_t<Rng>>
  + template<typename Rng, typename F>
  auto operator()(Rng &&rng, F fun) const ->
  CPP_ret(generate_result<safe_iterator_t<Rng>, F>)(
  requires Invocable<F&> && OutputRange<Rng, invoke_result_t<F &>>)
  