Uninstall a taxonomy vocabulary programmatically in Drupal 8.

nodemaker_vocabulary_delete.php

<?php

/**
 * @file
 * Contains various helper functions.
 */

use Drupal\taxonomy\Entity\Vocabulary;

/**
 * Helper function to remove a  vocabulary and all associated terms.
 *
 * During uninstall of a module containing a vocabulary with terms, neither are
 * removed automatically. Use this function to remove the vocabulary and terms
 * with any associated vocabulary.
 *
 * @code
 * function nodemaker_business_directory_uninstall() {
 *
 *   // Uninstall the MY_CUSTOM_VOCAB taxonomy.
 *   _nodemaker_vocabulary_delete('MY_CUSTOM_VOCAB');
 * }
 * @endcode
 *
 * @param string $vid
 *   - Vocabulary id (system name) of the vocabulary to be removed.
 */
function _nodemaker_vocabulary_delete($vid) {
  $vocab = Vocabulary::load($vid);
  if ($vocab) {
    $vocab->delete();
  }
}