[common.iter.types] Avoid "defining" typedef-names

Author: frederick-vs-ja

source/iterators.tex

@@ -5520,7 +5520,7 @@
 \pnum
 The nested \grammarterm{typedef-name} \tcode{iterator_category} of
 the specialization of \tcode{iterator_traits} for \tcode{common_iterator<I, S>}
-is defined if and only if \tcode{iter_difference_t<I>} is an integral type.
+is declared if and only if \tcode{iter_difference_t<I>} is an integral type.
 In that case,
 \tcode{iterator_category} denotes \tcode{forward_iterator_tag} if
 the \grammarterm{qualified-id} \tcode{iterator_traits<I>::iterator_category}