build: remove deprecated std::iterator usage

[mshabunin]

Fixes warnings during OpenCV build with C++17 standard (Ubuntu 24):

[3/2101] Building CXX object CMakeFiles/ade.dir/3rdparty/ade/ade-0.1.2d/sources/ade/source/memory_descriptor.cpp.o
In file included from /home/ubuntu/build/3rdparty/ade/ade-0.1.2d/sources/ade/include/ade/memory/memory_types.hpp:14,
                 from /home/ubuntu/build/3rdparty/ade/ade-0.1.2d/sources/ade/include/ade/memory/memory_descriptor.hpp:14,
                 from /home/ubuntu/build/3rdparty/ade/ade-0.1.2d/sources/ade/source/memory_descriptor.cpp:7:
/home/ubuntu/build/3rdparty/ade/ade-0.1.2d/sources/ade/include/ade/util/md_view.hpp:47:46: warning: 'template<class _Category, class _Tp, class _Distance, class _Pointer, class _Reference> struct std::iterator' is deprecated [-Wdeprecated-declarations]
   47 | class MdViewIteratorImpl final : public std::iterator<std::random_access_iterator_tag, DiffT>
      |                                              ^~~~~~~~

Note: perhaps there was a mistake - DiffT was used as a second template argument, meaning that it will be declared value_type. While in other places in this class different declarations val_t and diff_t exist, so I used them instead.

template<
    class Category,
    class T,
    class Distance = std::ptrdiff_t,
    class Pointer = T*,
    class Reference = T&
> struct iterator;

[dmatveev]

I don't think this class is used anywhere except tests, if it has tests, of course. Thanks a lot Maksim!