message: Simplify adaptor_cursor::mixin metaprogramming
diff: @@ -259,11 +259,7 @@ namespace ranges
  template<typename Adapt_>
  static meta::id<typename Adapt_::template mixin<basic_adaptor_mixin>> basic_adaptor_mixin_2_(int);
  - struct basic_adaptor_mixin_
  - : decltype(basic_adaptor_mixin_2_<Adapt>(42))
  - {};
  -
  - using mixin = meta::_t<basic_adaptor_mixin_>;
  + using mixin = meta::_t<decltype(basic_adaptor_mixin_2_<Adapt>(42))>;
  using base_t::first;
  using base_t::second;
  