Make easy-mmode-define-keymap obsolete

* lisp/emacs-lisp/easy-mmode.el (easy-mmode-define-keymap): Make
obsolete.
(define-minor-mode): Add comment.

lisp/emacs-lisp/easy-mmode.el

@@ -417,6 +417,8 @@ No problems result if this variable is not bound.
 	  `(defvar ,keymap-sym
 	     (let ((m ,keymap))
 	       (cond ((keymapp m) m)
+                     ;; FIXME: `easy-mmode-define-keymap' is obsolete,
+                     ;; so this form should also be obsolete somehow.
 		     ((listp m) (easy-mmode-define-keymap m))
 		     (t (error "Invalid keymap %S" m))))
 	     ,(format "Keymap for `%s'." mode-name)))
@@ -679,6 +681,7 @@ Valid keywords and arguments are:
   :group     Ignored.
   :suppress  Non-nil to call `suppress-keymap' on keymap,
              `nodigits' to suppress digits as prefix arguments."
+  (declare (obsolete define-keymap "29.1"))
   (let (inherit dense suppress)
     (while args
       (let ((key (pop args))