[temp.res.general] Grammatical parallelism: remove a stray "a" (#6796)

Author: Quuxplusone

source/templates.tex

@@ -4423,7 +4423,7 @@
 \end{itemize}
 \item a \grammarterm{decl-specifier} of the \grammarterm{decl-specifier-seq} of a
 \begin{itemize}
-\item \grammarterm{simple-declaration} or a \grammarterm{function-definition} in namespace scope,
+\item \grammarterm{simple-declaration} or \grammarterm{function-definition} in namespace scope,
 \item \grammarterm{member-declaration},
 \item \grammarterm{parameter-declaration} in a \grammarterm{member-declaration},
 \begin{footnote}