Double click prevention introduced in Drupal 7

Thanks @everkuil for your question. I've ran some tests and checked the source code - looks like drupal.form-single-submit built-in behavior does the same job (using the same principle) as webform_single_submit. So answering to your questions:

1. This module is no longer necessary (for Drupal 7.98+)
2. This module may interfere with new drupal behavior, but it should not break anything. Either webform_single_submit or drupal.form-single-submit would be executed first and prevent duplicate submission.