Removing getFormObject call from UserAccountFormFieldsTest

Problem/Motivation

protected function buildAccountForm($operation) {
    // @see HtmlEntityFormController::getFormObject()
    $entity_type = 'user';
    $fields = [];
    if ($operation != 'register') {
      $fields['uid'] = 2;
    }
    $entity = $this->container->get('entity_type.manager')
      ->getStorage($entity_type)
      ->create($fields);
    $this->container->get('entity_type.manager')
      ->getFormObject($entity_type, $operation)
      ->setEntity($entity);

    // @see EntityFormBuilder::getForm()
    return $this->container->get('entity.form_builder')->getForm($entity, $operation);
  }

Proposed resolution

code is repeated in \Drupal\Core\Entity\EntityFormBuilder::getForm() so the getFormObject call is not needed.

 protected function buildAccountForm($operation) {
    // @see HtmlEntityFormController::getFormObject()
    $entity_type = 'user';
    $fields = [];
    if ($operation != 'register') {
      $fields['uid'] = 2;
    }
    $entity = $this->container->get('entity_type.manager')
      ->getStorage($entity_type)
      ->create($fields);

    // @see EntityFormBuilder::getForm()
    return $this->container->get('entity.form_builder')->getForm($entity, $operation);
  }

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

None.

API changes

None.

Data model changes

None.