Move cl.el to lisp/obsolete

* lisp/emacs-lisp/cl.el: Move from here...
* lisp/obsolete/cl.el: ...to here.

* lisp/subr.el (do-after-load-evaluation): Use "deprecated" in the
message when loading packages from lisp/obsolete.

etc/NEWS

@@ -497,6 +497,8 @@ current and the previous or the next line, as before.
 
 * Changes in Specialized Modes and Packages in Emacs 27.1
 
+** The 'cl' package is now officially deprecated in favor of `cl-lib`.
+
 +++
 ** winner
 *** A new variable, 'winner-boring-buffers-regexp', has been added.

lisp/obsolete/cl.el

@@ -3,6 +3,7 @@
 ;; Copyright (C) 2012-2019 Free Software Foundation, Inc.
 
 ;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
+;; Deprecated-since: 27.1
 ;; Keywords: extensions
 
 ;; This file is part of GNU Emacs.

lisp/subr.el

@@ -4453,7 +4453,7 @@ This function is called directly from the C code."
            (package (intern (substring file 0
 			               (string-match "\\.elc?\\>" file))
                             obarray))
-	   (msg (format "Package %s is obsolete" package)))
+	   (msg (format "Package %s is deprecated" package)))
       ;; Cribbed from cl--compiling-file.
       (when (or (not (fboundp 'byte-compile-warning-enabled-p))
                 (byte-compile-warning-enabled-p 'obsolete package))