test: refactor test-http-write-empty-string to use arrow functions

In `test/parallel/test-http-write-empty-string.js`, callbacks use
anonymous closure functions. Replace them with arrow functions.

PR-URL: nodejs#24483
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-http-write-empty-string.js

@@ -38,16 +38,16 @@ const server = http.createServer(function(request, response) {
   this.close();
 });
 
-server.listen(0, common.mustCall(function() {
-  http.get({ port: this.address().port }, common.mustCall(function(res) {
+server.listen(0, common.mustCall(() => {
+  http.get({ port: server.address().port }, common.mustCall((res) => {
     let response = '';
 
     assert.strictEqual(res.statusCode, 200);
     res.setEncoding('ascii');
-    res.on('data', function(chunk) {
+    res.on('data', (chunk) => {
       response += chunk;
     });
-    res.on('end', common.mustCall(function() {
+    res.on('end', common.mustCall(() => {
       assert.strictEqual(response, '1\n2\n3\n');
     }));
   }));