[iterator.concept.iterator] Remove stray, mismatched parenthesis

Author: tkoeppe

source/iterators.tex

@@ -1354,7 +1354,7 @@
 to compare iterators with sentinels\iref{iterator.concept.sentinel}, to
 read\iref{iterator.concept.input} or write\iref{iterator.concept.output} values, or
 to provide a richer set of iterator movements (\ref{iterator.concept.forward},
-\ref{iterator.concept.bidir}, \ref{iterator.concept.random.access}).)
+\ref{iterator.concept.bidir}, \ref{iterator.concept.random.access}).
 
 \indexlibrary{\idxcode{Iterator}}%
 \begin{codeblock}