Mostly remove pre-CXX11 workarounds.

С++03 support was deprecated in 1.85 and now can be removed. This PR clears
many of workarounds, which are no longer needed now.

* Remove unused workaround macros (many of).
* Remove BOOST_STATIC_ASSERT usages.
* Minimize Boost::type_traits dependency (in favour of STL's type_traits).

Closes https://github.com/boostorg/iterator/pull/82.

Squashed commit of the following:

commit 741a627b73
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 12:13:05 2025 +0300

    Replace testers with standard metafunctions.

commit bf4cce6114
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 11:51:32 2025 +0300

    Refactor is_lvalue_iterator.hpp.

commit 8d080c6c58
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Jan 25 10:27:32 2025 +0300

    Remove more workarounds.

commit 5a4ba24d36
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sun Jan 19 16:38:30 2025 +0300

    Fixes.

commit fdfafce2b9
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Oct 26 15:06:43 2024 +0300

    Remove BOOST_NO_STRICT_ITERATOR_INTEROPERABILITY
    Correct static_assert messages.
    Fix messages & replace is_standard_layout with is_copy_constructible.

commit c69ac1408a
Author: Georgy Guminov <gogagum@gmail.com>
Date:   Sat Oct 26 14:48:51 2024 +0300

    Correct static_assert messages.

commit b5df827151
Author: Georqy Guminov <gogagum@gmail.com>
Date:   Sun Jun 23 16:12:29 2024 +0300

    Fixes. Remove some Boost.MPL usages. Remove unused includes.

commit 01fd35e9f8
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 17:14:21 2024 +0300

    abstract conjunction.

commit c02def8acf
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 16:35:43 2024 +0300

    return addressof & conjunction.

commit 3b3d162575
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 16:30:44 2024 +0300

    Make macro more readable.

commit 4ab19e045f
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 15:56:49 2024 +0300

    Add static_assert messages.

commit 82b5c44cd3
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Wed Jun 12 14:12:10 2024 +0300

    Return is iterator CXX17 test.

commit 2d58d65462
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Tue Jun 11 14:04:17 2024 +0300

    Omitted.

commit a0d04d9491
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Tue Jun 11 14:00:35 2024 +0300

    Replace move with static_cast

commit 4a49b8a1a2
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Mon Jun 10 21:38:53 2024 +0300

    Return BOOST_NOEXCEPT

commit 054c013bba
Author: Georgiy Guminov <gogagum@gmail.com>
Date:   Sun Jun 9 15:20:41 2024 +0300

    CXX11

include/boost/iterator/is_iterator.hpp

@@ -16,15 +16,15 @@
 
 #include <cstddef>
 #include <boost/config.hpp>
-#include <boost/type_traits/integral_constant.hpp>
-#include <boost/type_traits/negation.hpp>
-#include <boost/type_traits/conjunction.hpp>
 #include <boost/type_traits/is_complete.hpp>
-#include <boost/type_traits/is_function.hpp>
+#include <boost/iterator/detail/type_traits/conjunction.hpp>
+#include <boost/iterator/detail/type_traits/negation.hpp>
 #if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS)
 #include <iterator>
 #endif
 
+#include <type_traits>
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #pragma once
 #endif
@@ -59,56 +59,56 @@ no_type check(...);
 
 template< typename T >
 struct is_iterator_impl :
-    public boost::integral_constant<
+    public std::integral_constant<
         bool,
-        sizeof(has_iterator_category_detail::check< T >(0)) == sizeof(has_iterator_category_detail::yes_type)
+        sizeof(has_iterator_category_detail::check<T>(0)) == sizeof(has_iterator_category_detail::yes_type)
     >
 {
 };
 
 template< typename T >
 struct is_iterator_impl< T* > :
-    public boost::conjunction<
-        boost::is_complete< T >,
-        boost::negation< boost::is_function< T > >
+    public conjunction<
+        boost::is_complete<T>,
+        negation< std::is_function< T > >
     >::type
 {
 };
 
 template< typename T, typename U >
 struct is_iterator_impl< T U::* > :
-    public boost::false_type
+    public std::false_type
 {
 };
 
 template< typename T >
-struct is_iterator_impl< T& > :
-    public boost::false_type
+struct is_iterator_impl<T&> :
+    public std::false_type
 {
 };
 
 template< typename T, std::size_t N >
 struct is_iterator_impl< T[N] > :
-    public boost::false_type
+    public std::false_type
 {
 };
 
 #if !defined(BOOST_TT_HAS_WORKING_IS_COMPLETE)
 template< typename T >
 struct is_iterator_impl< T[] > :
-    public boost::false_type
+    public std::false_type
 {
 };
 
 template< >
 struct is_iterator_impl< void > :
-    public boost::false_type
+    public std::false_type
 {
 };
 
 template< >
 struct is_iterator_impl< void* > :
-    public boost::false_type
+    public std::false_type
 {
 };
 #endif // !defined(BOOST_TT_HAS_WORKING_IS_COMPLETE)