Disable user nick name in Drupal 8

custom_user.module.php

<?php
use \Drupal\user\UserInterface;
use \Drupal\Component\Utility\Random;

/**
 * Implements hook_ENTITY_TYPE_create().
 */
function custom_user_user_presave(UserInterface $entity) {
  $entity->setUsername($entity->getEmail());
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function custom_user_form_user_form_alter(&$form) {
  $form['account']['mail']['#required'] = TRUE;
  $form['account']['name']['#access'] = FALSE;
  $random = new Random();
  $form['account']['name']['#default_value'] = $random->name();
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function custom_user_form_user_register_form_alter(&$form) {
  custom_user_form_user_form_alter($form);
}