Remove sleep(5) in tests tearDown method when not necessary anymore

We had to add a sleep(5) in the DomainTestBase teardDown() method in order to have the tests passing on Drupal.org.

The patch was added in MR 162.

Once the problem is fixed on Drupal.org side, we can remove our temporary fix.

See https://www.drupal.org/project/gitlab_templates/issues/3500566#comment-1... 🐛 "Directory not empty" warning triggered by something in CI Active