Overriding the User Admin Form
===

I'm trying to override the `SonataUser/Admin/Model/UserAdmin`'s `configureFormFields()` because I need to remove some default fields from the admin form.
So I have copied the file `vendor/bundles/Sonata/UserBundle/Admin/Model/UserAdmin.php` in my bundle `app/Application/Sonata/UserBundle/Admin/Model/UserAdmin.php` and modified it. Then declared it as a service:

    # app/application/Sonata/UserBundle/Resources/config/services.yml
    services:
        application_user.registration.form.type:
            class: Application\Sonata\UserBundle\Admin\Model\UserAdmin
            arguments: [%sonata_user.model.user.class%]
            tags:
                - { name: form.type, alias: application_user_admin }

Now questions:
Am I doing right ? How can I tell sonata admin to use it ?