[zombie.names] Remove superfluous period (#6774)

Author: Andreas-Krug

source/lib-intro.tex

@@ -3088,7 +3088,7 @@
 \item \indexlibraryzombie{open_mode} \tcode{open_mode},
 \item \indexlibraryzombie{preferred} \tcode{preferred},
 \item \indexlibraryzombie{second_argument_type} \tcode{second_argument_type},
-\item \indexlibraryzombie{seek_dir} \tcode{seek_dir}, and.
+\item \indexlibraryzombie{seek_dir} \tcode{seek_dir}, and
 \item \indexlibraryzombie{strict} \tcode{strict}.
 \end{itemize}