Make XEmacs compat variable warning-level-aliases obsolete

* lisp/emacs-lisp/warnings.el (warning-level-aliases): Make obsolete.
(display-warning): Warn when using one of the warning levels defined
in above obsolete variable.  (Bug#44849)
* lisp/url/url-proxy.el (url-find-proxy-for-url): Replace obsolete
warning type 'critical with :error.

lisp/emacs-lisp/warnings.el

@@ -67,6 +67,7 @@ Level :debug is ignored by default (see `warning-minimum-level').")
 Each element looks like (ALIAS . LEVEL) and defines ALIAS as
 equivalent to LEVEL.  LEVEL must be defined in `warning-levels';
 it may not itself be an alias.")
+(make-obsolete-variable 'warning-level-aliases 'warning-levels "28.1")
 
 (define-obsolete-variable-alias 'display-warning-minimum-level
   'warning-minimum-level "28.1")
@@ -256,8 +257,10 @@ entirely by setting `warning-suppress-types' or
       (setq level :warning))
     (unless buffer-name
       (setq buffer-name "*Warnings*"))
-    (if (assq level warning-level-aliases)
-	(setq level (cdr (assq level warning-level-aliases))))
+    (with-suppressed-warnings ((obsolete warning-level-aliases))
+      (when-let ((new (cdr (assq level warning-level-aliases))))
+        (warn "Warning level `%s' is obsolete; use `%s' instead" level new)
+        (setq level new)))
     (or (< (warning-numeric-level level)
 	   (warning-numeric-level warning-minimum-log-level))
 	(warning-suppress-p type warning-suppress-log-types)

lisp/url/url-proxy.el

@@ -59,7 +59,7 @@
      ((string-match "^socks +" proxy)
       (concat "socks://" (substring proxy (match-end 0))))
      (t
-      (display-warning 'url (format "Unknown proxy directive: %s" proxy) 'critical)
+      (display-warning 'url (format "Unknown proxy directive: %s" proxy) :error)
       nil))))
 
 (autoload 'url-http "url-http")