Remove the gnus-union alias

* lisp/gnus/gnus-util.el (gnus-union): Remove.

lisp/gnus/gnus-group.el

@@ -1369,7 +1369,7 @@ if it is a string, only list groups matching REGEXP."
     (when (or gnus-group-listed-groups
 	      (and (>= level gnus-level-killed) (<= lowest gnus-level-killed)))
       (gnus-group-prepare-flat-list-dead
-       (gnus-union
+       (cl-union
 	not-in-list
 	(setq gnus-killed-list (sort gnus-killed-list 'string<))
 	:test 'equal)

lisp/gnus/gnus-util.el

@@ -1265,29 +1265,6 @@ If HASH-TABLE-P is non-nil, regards SEQUENCE as a hash table."
 (put 'gnus-with-output-to-file 'lisp-indent-function 1)
 (put 'gnus-with-output-to-file 'edebug-form-spec '(form body))
 
-(if (fboundp 'union)
-    (defalias 'gnus-union 'union)
-  (defun gnus-union (l1 l2 &rest keys)
-    "Set union of lists L1 and L2.
-If KEYS contains the `:test' and `equal' pair, use `equal' to compare
-items in lists, otherwise use `eq'."
-    (cond ((null l1) l2)
-	  ((null l2) l1)
-	  ((equal l1 l2) l1)
-	  (t
-	   (or (>= (length l1) (length l2))
-	       (setq l1 (prog1 l2 (setq l2 l1))))
-	   (if (eq 'equal (plist-get keys :test))
-	       (while l2
-		 (or (member (car l2) l1)
-		     (push (car l2) l1))
-		 (pop l2))
-	     (while l2
-	       (or (memq (car l2) l1)
-		   (push (car l2) l1))
-	       (pop l2)))
-	   l1))))
-
 (declare-function gnus-add-text-properties "gnus"
                   (start end properties &optional object))
 

lisp/gnus/mml-sec.el

@@ -557,7 +557,7 @@ Return keys."
   (let* ((usage-prefs (mml-secure-cust-usage-lookup context usage))
 	 (curr-fprs (cdr (assoc name (cdr usage-prefs))))
 	 (key-fprs (mapcar 'mml-secure-fingerprint keys))
-	 (new-fprs (gnus-union curr-fprs key-fprs :test 'equal)))
+	 (new-fprs (cl-union curr-fprs key-fprs :test 'equal)))
     (if curr-fprs
 	(setcdr (assoc name (cdr usage-prefs)) new-fprs)
       (setcdr usage-prefs (cons (cons name new-fprs) (cdr usage-prefs))))