RegistrationLinkAccessCheck dependency injection

Problem/Motivation

Use dependency injection for $user_settings = \Drupal::config('user.settings');

Proposed resolution

  /**
   * RegistrationLinkAccessCheck constructor.
   *
   * @param ConfigFactory $configFactory
   *   The Config Factory service.
   */
  public function __construct(ConfigFactory $configFactory) {
    $this->configFactory = $configFactory->get('user.settings');
  }

Remaining tasks

1. Create patch
2. Review/RTBC
3. Commit

User interface changes

- None

API changes

- None