Site Health: Explicitly deprecate WP_Debug_Data::get_sizes(), unused since WP 5.6.

Follow-up to [49154], [60272].

Props yashjawale, dhruvang21, ankitkumarshah, SergeyBiryukov.
Fixes #63516.

git-svn-id: https://develop.svn.wordpress.org/trunk@60274 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/class-wp-debug-data.php

@@ -1866,6 +1866,8 @@ public static function get_database_size() {
 	 * @return array The sizes of the directories, also the database size and total installation size.
 	 */
 	public static function get_sizes() {
+		_deprecated_function( __METHOD__, '5.6.0', 'WP_REST_Site_Health_Controller::get_directory_sizes()' );
+
 		$size_db    = self::get_database_size();
 		$upload_dir = wp_get_upload_dir();