[std.iterator.tags] Use "declare" for typedef-names

Author: frederick-vs-ja

source/iterators.tex

@@ -2768,7 +2768,7 @@
 For every iterator of type
 \tcode{I},
 \tcode{iterator_traits<I>::it\-er\-a\-tor_ca\-te\-go\-ry}
-shall be defined to be a category tag that describes the
+shall be declared to be a category tag that describes the
 iterator's behavior.
 Additionally,
 \tcode{iterator_traits<I>::it\-er\-a\-tor_con\-cept}