Additional 'Update Manager' deprecations

In addition to the changes described at authorize.php, the FileTransfer and Updater systems, and all related code is deprecated, additional services, functions and a theme template are deprecated:

1. The update.root service and core/modules/update/src/UpdateRoot.php
2. _update_manager_cache_directory()
3. _update_manager_extract_directory()
4. _update_manager_unique_identifier()
5. update_clear_update_disk_cache()
6. update_delete_file_if_stale()
7. The authorize-report theme template, authorize-report.html.twig (from both system and stable9 theme), and template_preprocess_authorize_report()

There is no replacement. Use composer to manage the code for Drupal sites.

update_clear_update_disk_cache() used to be called via hook_cron(), but that is no longer the case. Sites that haven't used the Update Manager should not have any files in this cache. A post update method is provided, update_post_update_clear_disk_cache(), to remove directories named "update-cache-*" and "update-extraction-*" (and all of their contents) in the site's temporary directory on disk.