Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / modules / user / tests / modules / user_form_test / user_form_test.routing.yml

user_form_test.cancel:
  path: '/user_form_test_cancel/{user}'
  defaults:
    _entity_form: 'user.cancel'
  requirements:
    _permission: 'cancel other accounts'