Remove a Webform Submit Handler
/** @var \Drupal\webform\Plugin\WebformHandlerManagerInterface $handler_manager */
$webformStorage = \Drupal::entityTypeManager()->getStorage('webform');
foreach ($webformStorage->loadMultiple() as $webform) {
if ($webform->getHandlers()->has('email')) {
$webform->deleteWebformHandler($webform->getHandler('email'));
$webform->save();
}
}