message: simplify sfinae
diff: @@ -269,7 +269,7 @@ namespace ranges
  struct any_cursor_interface;
  template<typename Ref, category Cat>
  - struct any_cursor_interface<Ref, Cat, meta::_t<std::enable_if<(Cat & category::mask) == category::forward>>>
  + struct any_cursor_interface<Ref, Cat, meta::if_c<(Cat & category::mask) == category::forward>>
  {
  virtual ~any_cursor_interface() = default;
  virtual any_ref iter() const = 0; // returns a const ref to the cursor's wrapped iterator
  @@ -280,14 +280,14 @@ namespace ranges
  template<typename Ref, category Cat>
  - struct any_cursor_interface<Ref, Cat, meta::_t<std::enable_if<(Cat & category::mask) == category::bidirectional>>>
  + struct any_cursor_interface<Ref, Cat, meta::if_c<(Cat & category::mask) == category::bidirectional>>
  : any_cursor_interface<Ref, category::forward>
  {
  virtual void prev() = 0;
  };
  template<typename Ref, category Cat>
  - struct any_cursor_interface<Ref, Cat, meta::_t<std::enable_if<(Cat & category::mask) == category::random_access>>>
  + struct any_cursor_interface<Ref, Cat, meta::if_c<(Cat & category::mask) == category::random_access>>
  : any_cursor_interface<Ref, category::bidirectional>
  {
  virtual void advance(std::ptrdiff_t) = 0;
  @@ -564,7 +564,7 @@ namespace ranges
  // input and not forward
  template<typename Ref, category Cat>
  - struct any_view<Ref, Cat, meta::_t<std::enable_if<(Cat & category::forward) == category::input>>>
  + struct any_view<Ref, Cat, meta::if_c<(Cat & category::forward) == category::input>>
  : view_facade<any_view<Ref, Cat, void>, (Cat & category::sized) == category::sized ? finite : unknown>
  {
  friend range_access;
  