Remove superfluous index entry for posix.popen(); no longer

appropriate since popen() is only documented in os.

Doc/lib/libselect.tex

@@ -43,7 +43,6 @@ objects (e.g. \code{sys.stdin}, or objects returned by
 \function{open()} or \function{os.popen()}), socket objects
 returned by \function{socket.socket()},%
 \withsubitem{(in module socket)}{\ttindex{socket()}}
-\withsubitem{(in module posix)}{\ttindex{popen()}}
 \withsubitem{(in module os)}{\ttindex{popen()}}
 and the module \module{stdwin}\refbimodindex{stdwin} which happens to
 define a function \function{fileno()}%