message: Remove specialization of std::is_integral in safe_int
  No, no, no! BAD!
  (Also, don't check `is_literal` since it's deprecated in C++17.)
diff: @@ -290,8 +290,6 @@ namespace ranges
  template<typename Int>
  using make_safe_int_t = typename make_safe_int<Int>::type;
  - static_assert(std::is_literal_type<safe_int<int>>::value, "");
  -
  template<typename SignedInteger>
  constexpr SignedInteger safe_int<SignedInteger>::pos_inf_;
  @@ -305,11 +303,6 @@ namespace ranges
  namespace std
  {
  - template<typename T>
  - struct is_integral<::ranges::v3::safe_int<T>>
  - : is_integral<T>
  - {};
  -
  template<typename T>
  class numeric_limits<::ranges::v3::safe_int<T>>
  : public numeric_limits<T>
  