13962 disabling work package status does not work for details pane

[``* `#13962`Disabling work package status does not work in details pane``](https://www.openproject.org/work_packages/13962)
@hschink this would be a little more "Rubyish":

```ruby
def percentage_done
  represented.percentage_done if Setting.work_package_done_ratio == 'disabled'
end
```