Remove the 'M-o' ('facemap-keymap') binding experimentally

* doc/lispref/maps.texi (Standard Keymaps):
* doc/lispref/keymaps.texi (Prefix Keys): Remove mentions.

* etc/facemenu-removal.txt: New temporary file.

* lisp/loadup.el: Don't load facemenu.el.
(removed-facemenu-command): New command.
(facemenu-keymap-restore): New function.

* lisp/textmodes/text-mode.el (center-paragraph): Remove binding.
(center-line): Remove binding.

doc/lispref/keymaps.texi

@@ -573,12 +573,6 @@ key.
 @code{search-map} is the global keymap used for the @kbd{M-s} prefix
 key.
 
-@item
-@cindex @kbd{M-o}
-@vindex facemenu-keymap
-@code{facemenu-keymap} is the global keymap used for the @kbd{M-o}
-prefix key.
-
 @item
 The other Emacs prefix keys are @kbd{C-x @@}, @kbd{C-x a i}, @kbd{C-x
 @key{ESC}} and @kbd{@key{ESC} @key{ESC}}.  They use keymaps that have

doc/lispref/maps.texi

@@ -53,9 +53,6 @@ A sparse keymap for subcommands of the prefix @kbd{C-x r}.@*
 @item esc-map
 A full keymap for @key{ESC} (or @key{Meta}) commands.
 
-@item facemenu-keymap
-A sparse keymap used for the @kbd{M-o} prefix key.
-
 @item function-key-map
 The parent keymap of all @code{local-function-key-map} (q.v.@:) instances.
 

etc/NEWS

@@ -2048,6 +2048,11 @@ first).
 
 * Incompatible Editing Changes in Emacs 28.1
 
+** The 'M-o' ('facemanu-keymap') global binding has been removed.
+
+** The 'M-o M-s' and 'M-o M-S' global bindings have been removed.
+Use 'M-x center-line' and 'M-x center-paragraph' instead.
+
 ** In 'f90-mode', the backslash character ('\') no longer escapes.
 For about a decade, the backslash character has no longer had a
 special escape syntax in Fortran F90.  To get the old behaviour back,

etc/facemenu-removal.txt

@@ -0,0 +1,20 @@
+`facemenu-keymap' (normally bound to `M-o') has been disabled.
+==============================================================
+
+We've disabled the normal `M-o' keymap for a month (until March the
+10th, 2021) in the development version of Emacs to see whether anybody
+uses this feature.
+
+If the removal of this key binding doesn't annoy too many people, the
+plan is to then leave the it unbound, for usage by third-party
+packages and users.
+
+If you wish to restore the binding during the trial period, you can
+put the following in your .emacs file:
+
+(facemenu-keymap-restore)
+
+After the trial period is over, the function will be removed.
+
+If you wish to protest the removal of the `M-o' key binding, please
+send your thoughts to the emacs-devel@gnu.org mailing list.

lisp/loadup.el

@@ -253,9 +253,6 @@
 (load "startup")
 (load "term/tty-colors")
 (load "font-core")
-;; facemenu must be loaded before font-lock, because `facemenu-keymap'
-;; needs to be defined when font-lock is loaded.
-(load "facemenu")
 (load "emacs-lisp/syntax")
 (load "font-lock")
 (load "jit-lock")
@@ -477,6 +474,28 @@ lost after dumping")))
 ;; Make sure we will attempt bidi reordering henceforth.
 (setq redisplay--inhibit-bidi nil)
 
+
+;; Experimental feature removal.
+(define-key global-map "\M-o" #'removed-facemenu-command)
+
+(defun removed-facemenu-command ()
+  "Transition command during test period for facemenu removal."
+  (interactive)
+  (switch-to-buffer "*Facemenu Removal*")
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert-file-contents
+     (expand-file-name "facemenu-removal.txt" data-directory)))
+  (goto-char (point-min))
+  (special-mode))
+
+(defun facemenu-keymap-restore ()
+  "Restore the facemenu keymap."
+  (require 'facemenu)
+  (define-key facemenu-keymap "\eS" 'center-paragraph)
+  (define-key facemenu-keymap "\es" 'center-line))
+
+
 (if dump-mode
     (let ((output (cond ((equal dump-mode "pdump") "emacs.pdmp")
                         ((equal dump-mode "dump") "emacs")

lisp/textmodes/text-mode.el

@@ -169,8 +169,6 @@ both existing buffers and buffers that you subsequently create."
 	     (if enable-mode "enabled" "disabled"))))
 
 
-(define-key facemenu-keymap "\eS" 'center-paragraph)
-
 (defun center-paragraph ()
   "Center each nonblank line in the paragraph at or after point.
 See `center-line' for more info."
@@ -198,8 +196,6 @@ See `center-line' for more info."
 	    (center-line))
 	(forward-line 1)))))
 
-(define-key facemenu-keymap "\es" 'center-line)
-
 (defun center-line (&optional nlines)
   "Center the line point is on, within the width specified by `fill-column'.
 This means adjusting the indentation so that it equals