views: fix image create backtrace

Fix backtrace caused by efd0b8ac
Don't access the field scopes in ImageCreateForm as it does not
exist.

ogcp/views.py

@@ -2357,8 +2357,6 @@ def action_image_create():
                                    if client_repo_id == repo['id']]
         form.repository.render_kw = {'readonly': True}
 
-        form.scopes.choices = get_available_centers()
-
         scopes, clients = get_scopes(set(ips))
         return render_template('actions/image_create.html', form=form,
                                scopes=scopes)