Start deleting ckeditor4

Closes #3239012

core/modules/ckeditor5/src/Annotation/CKEditor4To5Upgrade.php

-<?php
-
-declare(strict_types = 1);
-
-namespace Drupal\ckeditor5\Annotation;
-
-use Drupal\Component\Annotation\Plugin;
-
-/**
- * Defines a CKEditor4To5Upgrade annotation object.
- *
- * Plugin Namespace: Plugin\CKEditor4To5Upgrade.
- *
- * @see \Drupal\ckeditor5\Plugin\CKEditor5PluginInterface
- * @see \Drupal\ckeditor5\Plugin\CKEditor5PluginManagerInterface
- * @see plugin_api
- *
- * @Annotation
- */
-class CKEditor4To5Upgrade extends Plugin {
-
-  /**
-   * The plugin ID.
-   *
-   * @var string
-   */
-  public $id;
-
-  /**
-   * The CKEditor 4 buttons for which an upgrade path is provided.
-   *
-   * @var string[]
-   */
-  public $cke4_buttons;
-
-  /**
-   * The CKEditor 4 plugins for whose settings an upgrade path is provided.
-   *
-   * @var string[]
-   */
-  public $cke4_plugin_settings;
-
-  /**
-   * The CKEditor 5 plugins with configurable subset with upgrade path provided.
-   *
-   * @var string[]
-   */
-  public $cke5_plugin_elements_subset_configuration;
-
-}