fix a js error intoduced by the no-vellum feature

if it wasn't enabled, you'd see

```
Uncaught ReferenceError: Unable to parse bindings.
Bindings value: attr: {href: '#' + id}, css: {collapsed: reallyCollapse}
Message: id is not defined
```

in the console every time you load a form settings page.

To my knowledge this didn't cause any user-facing errors.