[iterator.traits] An implementation that provides __far pointers doesn't need

the standard to tell it (non-normatively) how to implement them.

Fixes #260.

Author: zygoloid

source/iterators.tex

@@ -917,27 +917,6 @@
 }
 \end{codeblock}
 
-\pnum
-\enternote
-If there is an additional pointer type
-\tcode{\,\xname{far}}
-such that the difference of two
-\tcode{\,\xname{far}}
-is of type
-\tcode{long},
-an implementation may define
-
-\begin{codeblock}
-  template<class T> struct iterator_traits<T @\xname{far}@*> {
-    typedef long difference_type;
-    typedef T value_type;
-    typedef T @\xname{far}@* pointer;
-    typedef T @\xname{far}@& reference;
-    typedef random_access_iterator_tag iterator_category;
-  };
-\end{codeblock}
-\exitnote
-
 \pnum
 \enterexample
 To implement a generic