Backport commit 797ee5871 from Emacs

The convention is that a file with Author: but not Maintainer:
means the author is a maintainer, which makes it confusing
when a file lists the same person as author and maintainer.
Avoid the confusion by removing the duplicate Maintainer: line.

Remove Maintainer: when it duplicates Author:
797ee5871e458d6d97f57a24405412a053f5ef32
Paul Eggert
Sun May 26 01:00:15 2019 -0700

lisp/org.el

@@ -4,7 +4,6 @@
 ;; Copyright (C) 2004-2019 Free Software Foundation, Inc.
 ;;
 ;; Author: Carsten Dominik <carsten at orgmode dot org>
-;; Maintainer: Carsten Dominik <carsten at orgmode dot org>
 ;; Keywords: outlines, hypermedia, calendar, wp
 ;; Homepage: https://orgmode.org
 ;; Version: 9.2.3