Remove redundant requires of 'button'

* lisp/apropos.el:
* lisp/emacs-lisp/cl-print.el:
* lisp/emacs-lisp/debug.el:
* lisp/emacs-lisp/ert.el:
* lisp/emacs-lisp/shadow.el:
* lisp/facemenu.el:
* lisp/help-mode.el:
* lisp/man.el:
* lisp/progmodes/etags.el:
* lisp/textmodes/bibtex.el:
* lisp/woman.el: Don't require 'button'; it is preloaded since version
23.1.

lisp/emacs-lisp/cl-print.el

@@ -33,8 +33,6 @@
 
 ;;; Code:
 
-(require 'button)
-
 (defvar cl-print-readably nil
   "If non-nil, try and make sure the result can be `read'.")
 

lisp/emacs-lisp/debug.el

@@ -29,7 +29,6 @@
 
 (require 'cl-lib)
 (require 'backtrace)
-(require 'button)
 
 (defgroup debugger nil
   "Debuggers and related commands for Emacs."

lisp/emacs-lisp/ert.el

@@ -58,7 +58,6 @@
 ;;; Code:
 
 (require 'cl-lib)
-(require 'button)
 (require 'debug)
 (require 'backtrace)
 (require 'easymenu)

lisp/emacs-lisp/shadow.el

@@ -183,7 +183,6 @@ See the documentation for `list-load-path-shadows' for further information."
 	buffer-read-only t))
 
 ;; TODO use text-properties instead, a la dired.
-(require 'button)
 (define-button-type 'load-path-shadows-find-file
   'follow-link t
 ;;  'face 'default