http: convert utcDate to use setTimeout

A sort-of follow-up to #17704, this
removes the last internal use of enroll().

PR-URL: #17800
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/http.js

@@ -1,20 +1,21 @@
 'use strict';
 
-const timers = require('timers');
+const { setUnrefTimeout } = require('internal/timers');
 
 var dateCache;
 function utcDate() {
   if (!dateCache) {
     const d = new Date();
     dateCache = d.toUTCString();
-    timers.enroll(utcDate, 1000 - d.getMilliseconds());
-    timers._unrefActive(utcDate);
+
+    setUnrefTimeout(resetCache, 1000 - d.getMilliseconds());
   }
   return dateCache;
 }
-utcDate._onTimeout = function() {
+
+function resetCache() {
   dateCache = undefined;
-};
+}
 
 function ondrain() {
   if (this._httpMessage) this._httpMessage.emit('drain');