test: Update test-http-parser-free to use countdown timer

PR-URL: #17322
Refs: #17169
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/parallel/test-http-parser-free.js

@@ -2,13 +2,15 @@
 require('../common');
 const assert = require('assert');
 const http = require('http');
+const Countdown = require('../common/countdown');
 const N = 100;
-let responses = 0;
 
 const server = http.createServer(function(req, res) {
   res.end('Hello');
 });
 
+const countdown = new Countdown(N, () => server.close());
+
 server.listen(0, function() {
   http.globalAgent.maxSockets = 1;
   let parser;
@@ -21,15 +23,9 @@ server.listen(0, function() {
           assert.strictEqual(req.parser, parser);
         }
 
-        if (++responses === N) {
-          server.close();
-        }
+        countdown.dec();
         res.resume();
       });
     })(i);
   }
 });
-
-process.on('exit', function() {
-  assert.strictEqual(responses, N);
-});