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'
-    }
-  );
-});

package.json

@@ -16,7 +16,6 @@
     "test-api": "mocha \"**/*.api.js\"",
     "test-unit": "node ./bin/test.js",
     "build": "tsc -b ./tsconfig.all.json",
-    "postbuild": "node ./bin/packageAddons.js",
     "prepare": "npm run build",
     "prepublishOnly": "npm run package",
     "watch": "tsc -b -w ./tsconfig.all.json --preserveWatchOutput",