fix: remove double registration from server-bundle.js template

Author: ihabadham

lib/generators/react_on_rails/templates/base/base/app/javascript/packs/server-bundle.js

@@ -1,8 +1 @@
-import ReactOnRails from 'react-on-rails';
-
-import HelloWorld from '../src/HelloWorld/HelloWorldServer';
-
-// This is how react_on_rails can see the HelloWorld in the browser.
-ReactOnRails.register({
-  HelloWorld,
-});
+// Placeholder comment - auto-generated imports will be prepended here by react_on_rails:generate_packs