How to programmatically delete a Webform Submissions in Drupal 8

Code snippet that can be used to programmatically delete a Webform Submissions in Drupal 8. 

$query = \Drupal::entityQuery('webform_submission')
  ->condition('webform_id', $WEBFORM_ID)
  ->accessCheck(FALSE);

$result = $query->execute();
foreach ($result as $item) {
  $submission = \Drupal\webform\Entity\WebformSubmission::load($item);
  $submission->delete();
}

if you want to programmatically delete a Webform from your website you can use code like this:

$webform = \Drupal::entityTypeManager()->getStorage('webform')->load($WEBFORM_ID);
if ($webform) {
  $webform->delete();
}

Example how to delete the default contact webform:

$webform = \Drupal::entityTypeManager()->getStorage('webform')->load('contact');
if ($webform) {
  $webform->delete();
}