Remove some references to XEmacs

* lisp/emulation/viper-cmd.el (viper-start-R-mode):
* lisp/emulation/viper-init.el (viper-window-display-p):
* lisp/emulation/viper-mous.el (viper-surrounding-word):
* lisp/mail/footnote.el (footnote-mode):
* lisp/textmodes/reftex-index.el: Remove some comments referring to
XEmacs.

lisp/emulation/viper-cmd.el

@@ -2311,7 +2311,6 @@ problems."
   (viper-downgrade-to-insert))
 
 (defun viper-start-R-mode ()
-  ;; Leave arg as 1, not t: XEmacs insists that it must be a pos number
   (overwrite-mode 1)
   (add-hook
    'viper-post-command-hooks #'viper-R-state-post-command-sentinel t 'local)

lisp/emulation/viper-init.el

@@ -44,7 +44,6 @@
 
 (define-obsolete-function-alias 'viper-device-type #'window-system "27.1")
 
-;; in XEmacs: device-type is tty on tty and stream in batch.
 (defun viper-window-display-p ()
   (and window-system (not (memq window-system '(tty stream pc)))))
 

lisp/emulation/viper-mous.el

@@ -198,8 +198,7 @@ is ignored."
 
 	 (setq result (buffer-substring word-beg (point))))
        ) ; if
-     ;; XEmacs doesn't have set-text-properties, but there buffer-substring
-     ;; doesn't return properties together with the string, so it's not needed.
+     ;; FIXME: Use `buffer-substring-no-properties' above instead?
      (set-text-properties 0 (length result) nil result)
      result))
 

lisp/mail/footnote.el

@@ -898,7 +898,7 @@ play around with the following keys:
     (make-local-variable 'footnote-end-tag)
     (make-local-variable 'adaptive-fill-function)
 
-    ;; Filladapt was an XEmacs package which is now in GNU ELPA.
+    ;; Filladapt is a GNU ELPA package.
     (when (boundp 'filladapt-token-table)
       ;; add tokens to filladapt to match footnotes
       ;; 1] xxxxxxxxxxx x x x or [1] x x x x x x x

lisp/textmodes/reftex-index.el

@@ -29,9 +29,7 @@
 
 (require 'reftex)
 
-;; START remove for XEmacs release
 (defvar TeX-master)
-;; END remove for XEmacs release
 
 ;;;###autoload
 (defun reftex-index-selection-or-word (&optional arg phrase)