Remove packageAddons step on install

It's not needed when the demo doesn't use it

bin/packageAddons.js

@@ -1,19 +0,0 @@
-/**
- * Copyright (c) 2019 The xterm.js authors. All rights reserved.
- * @license MIT
- */
-
-const cp = require('child_process');
-const path = require('path');
-const fs = require('fs');
-
-const addons = fs.readdirSync(path.resolve(__dirname, '../addons'));
-addons.forEach(addon => {  
-  cp.spawnSync(
-    'npm', ['run', 'package'],
-    {
-      cwd: path.resolve(__dirname, `../addons/${addon}`),
-      stdio: 'inherit'
-    }
-  );
-});