fs: use _final() for fs.WriteStream

use _final() method instead of once 'finish' event.

PR-URL: #20562
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/fs.js

@@ -2214,17 +2214,17 @@ function WriteStream(path, options) {
 
   if (typeof this.fd !== 'number')
     this.open();
-
-  // dispose on finish.
-  this.once('finish', function() {
-    if (this.autoClose) {
-      this.destroy();
-    }
-  });
 }
 
 fs.FileWriteStream = fs.WriteStream; // support the legacy name
 
+WriteStream.prototype._final = function(callback) {
+  if (this.autoClose) {
+    this.destroy();
+  }
+
+  callback();
+};
 
 WriteStream.prototype.open = function() {
   fs.open(this.path, this.flags, this.mode, (er, fd) => {