Adjust tests to work with composer autoloader

tests/bootstrap.php

@@ -10,10 +10,4 @@
  * file that was distributed with this source code.
  */
 
-require __DIR__.'/../src/Composer/Autoload/ClassLoader.php';
-
-$loader = new Composer\Autoload\ClassLoader();
-$loader->add('Composer\\', dirname(__DIR__).'/src/');
-$loader->add('Symfony\\Component\\', dirname(__DIR__).'/src/');
-$loader->add('Composer_', dirname(__DIR__).'/src/');
-$loader->register();
+require __DIR__.'/../vendor/.composer/autoload.php';