Remove unused deprecated includes

A comment in boost/iterator.hpp and boost/detail/iterator.hpp mentions that
the files are obsolete and will be deprecated. All they do is pull some types
from namespace std into namespace boost.

include/boost/pointee.hpp

@@ -20,6 +20,8 @@
 # include <boost/mpl/if.hpp>
 # include <boost/mpl/eval_if.hpp>
 
+#include <iterator>
+
 namespace boost {
 
 namespace detail
@@ -33,7 +35,7 @@ namespace detail
   template <class Iterator>
   struct iterator_pointee
   {
-      typedef typename iterator_traits<Iterator>::value_type value_type;
+      typedef typename std::iterator_traits<Iterator>::value_type value_type;
 
       struct impl
       {