Update comment in header of errcodes.txt
Update comment in header of errcodes.txt

This file mentions all the files generated from it, but missed that
errcodes-list.sgml is no more, while errcodes-table.sgml is.

Author: Noriyoshi Shinoda
Discussion: ec1ba75b86822d59333142f0287d5bc0e2307c44@TU4PR8401MB0430.NAMPRD84.PROD.OUTLOOK.COM

lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,adam8157/gpdb,50wu/gpdb