Fixes errors in constraint delete form where ConstraintDelete throws PHP warnings because the form array defines #validate but the class does not include a validate method:
Warning: call_user_func_array() expects parameter 1 to be a valid callback, class 'Drupal\password_policy\Form\ConstraintDelete' does not have a method 'validate' in Drupal\Core\Form\FormValidator->executeValidateHandlers() (line 88 of [...]/core/lib/Drupal/Core/Form/FormValidator.php).
Fixes a bug where the title of the ConstraintDelete form is missing the constraint title.