Remove usage of the deprecation HttpKernel base extension class

This bundle does not rely on the extra (deprecated) features provided in
the HttpKernel base class.

src/DependencyInjection/StofDoctrineExtensionsExtension.php

@@ -5,8 +5,8 @@
 use Symfony\Component\Cache\Adapter\ArrayAdapter;
 use Symfony\Component\Config\Loader\LoaderInterface;
 use Symfony\Component\DependencyInjection\Alias;
-use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 use Symfony\Component\Config\Definition\Processor;
+use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\ContainerBuilder;