http: convert utcDate to use setTimeout

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

Author: Fishrock123

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(timeout, 1000 - d.getMilliseconds());
   }
   return dateCache;
 }
-utcDate._onTimeout = function() {
+
+function timeout() {
   dateCache = undefined;
-};
+}
 
 function ondrain() {
   if (this._httpMessage) this._httpMessage.emit('drain');