MDL-76055 libraries: Autoload phpxmlrpc and verify it works

Also, we can now safely remove Autoloader.php, because
Moodle PSR-4 autoloader has taken control, so document
and test it too.

lib/phpxmlrpc/Autoloader.php

@@ -1,36 +0,0 @@
-<?php
-
-namespace PhpXmlRpc;
-
-/**
- * In the unlikely event that you are not using Composer to manage class autoloading, here's an autoloader for this lib.
- * For usage, see any file in the demo/client directory
- */
-class Autoloader
-{
-    /**
-     * Registers PhpXmlRpc\Autoloader as an SPL autoloader.
-     *
-     * @param bool $prepend Whether to prepend the autoloader or not.
-     */
-    public static function register($prepend = false)
-    {
-        spl_autoload_register(array(__CLASS__, 'autoload'), true, $prepend);
-    }
-
-    /**
-     * Handles autoloading of classes.
-     *
-     * @param string $class A class name.
-     */
-    public static function autoload($class)
-    {
-        if (0 !== strpos($class, 'PhpXmlRpc\\')) {
-            return;
-        }
-
-        if (is_file($file = __DIR__ . str_replace(array('PhpXmlRpc\\', '\\'), '/', $class).'.php')) {
-            require $file;
-        }
-    }
-}

lib/phpxmlrpc/readme_moodle.txt

@@ -11,6 +11,8 @@ To update:
 - Download or checkout it.
 - Delete the contents on the lib/phpxmlrpc directory (but this file) completely.
 - Copy the /src directory contents of the library to lib/phpxmlrpc.
+- Remove the following files:
+  - Autoloader.php
 - Edit this file and update the release and commit details below.
 - Edit lib/thirdpartylibs.xml and update the information details too.