It's still used on the `move_document` page...

```
john-moz@mozilla:kuma> ag-class btn-discard
apps/wiki/templates/wiki/move_document.html:81:          <li><a class="btn-discard" href="{{ url('wiki.document', document.full_path, locale=document.locale) }}">{{ _('Cancel') }}</a></li>
```

...but we already have `.button.negative` for that. I will update the page move cancel button to use those classes. Great catch!