test: deflake test-http-remove-header-stays-removed

Instead of relying on a timer, verify that `socket.end()` is called when
the `'finish'` event is emitted on the `ServerResponse` object.

PR-URL: #55004
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jake Yuesong Li <jake.yuesong@gmail.com>

test/parallel/test-http-remove-header-stays-removed.js

@@ -25,7 +25,9 @@ const assert = require('assert');
 
 const http = require('http');
 
-const server = http.createServer(function(request, response) {
+const server = http.createServer(common.mustCall(function(request, response) {
+  const socket = response.socket;
+
   // Removed headers should stay removed, even if node automatically adds them
   // to the output:
   response.removeHeader('connection');
@@ -36,32 +38,29 @@ const server = http.createServer(function(request, response) {
   response.removeHeader('date');
   response.setHeader('date', 'coffee o clock');
 
-  response.end('beep boop\n');
-});
-
-let response = '';
+  response.on('finish', common.mustCall(function() {
+    // The socket should be closed immediately, with no keep-alive, because
+    // no content-length or transfer-encoding are used.
+    assert.strictEqual(socket.writableEnded, true);
+  }));
 
-process.on('exit', function() {
-  assert.strictEqual(response, 'beep boop\n');
-  console.log('ok');
-});
+  response.end('beep boop\n');
+}));
 
 server.listen(0, function() {
   http.get({ port: this.address().port }, function(res) {
     assert.strictEqual(res.statusCode, 200);
     assert.deepStrictEqual(res.headers, { date: 'coffee o clock' });
 
+    let response = '';
     res.setEncoding('ascii');
     res.on('data', function(chunk) {
       response += chunk;
-      if (response === 'beep boop\n') {
-        setTimeout(function() {
-          // The socket should be closed immediately, with no keep-alive, because
-          // no content-length or transfer-encoding are used:
-          assert.strictEqual(res.socket.closed, true);
-          server.close();
-        }, common.platformTimeout(15));
-      }
+    });
+
+    res.on('end', function() {
+      assert.strictEqual(response, 'beep boop\n');
+      server.close();
     });
   });
 });