Remove deprecated function views_get_enabled_display_extenders

Remove deprecated function views_get_enabled_display_extenders from views module.

/**
 * Get enabled display extenders.
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
 *   Use \Drupal\views\Views::getEnabledDisplayExtenders().
 */
function views_get_enabled_display_extenders() {
  return Views::getEnabledDisplayExtenders();
}