Remove last XEmacs compat code from ERC

* lisp/erc/erc-dcc.el (erc-dcc-member): Remove XEmacs compat code.
* lisp/erc/erc-goodies.el (erc-move-to-prompt-setup): Doc fix;
remove spurious reference to XEmacs; this is needed also for
Emacs.

lisp/erc/erc-dcc.el

@@ -183,9 +183,7 @@ compared with `erc-nick-equal-p' which is IRC case-insensitive."
           (let ((prop (car prem))
                 (val (cadr prem)))
             (setq prem (cddr prem)
-                  ;; plist-member is a predicate in xemacs
-                  test (and (plist-member elt prop)
-                            (plist-get elt prop)))
+                  test (cadr (plist-member elt prop)))
             ;; if the property exists and is equal, we continue, else, try the
             ;; next element of the list
             (or (and (eq prop :nick) (if (>= emacs-major-version 28)

lisp/erc/erc-goodies.el

@@ -137,7 +137,7 @@ Put this function on `erc-insert-post-hook' and/or `erc-send-post-hook'."
     (goto-char (point-max))))
 
 (defun erc-move-to-prompt-setup ()
-  "Initialize the move-to-prompt module for XEmacs."
+  "Initialize the move-to-prompt module."
   (add-hook 'pre-command-hook #'erc-move-to-prompt nil t))
 
 ;;; Keep place in unvisited channels