drupal_classloader() removed

The function drupal_classloader() was removed.

Even though module namespaces are registered automatically it could be used in the rare case where an additional namespace needs to be registered and drupal_classloader_register() was not adequate.

For this, the class_loader service should be used directly now.

For example:

// Drupal 8 before this change
drupal_classloader->addPsr('Some\Custom\Namespace', array(drupal_get_path('module', 'mymodule') . '/some/directory'));

// Drupal 8 after this change. (Works before the change as well.)
\Drupal::service('class_loader')->addPsr('Some\Custom\Namespace', array(drupal_get_path('module', 'mymodule') . '/some/directory'));