minor #17146 Do not use HttpKernel Extension when not needed for 2.7 (Tobion)

This PR was merged into the 2.7 branch.

Discussion
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Do not use HttpKernel Extension when not needed for 2.7

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

#17145 for new stuff in 2.7

Commits
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cc64c54 Do not use HttpKernel Extension when not needed for 2.7

src/Symfony/Bundle/DebugBundle/DependencyInjection/DebugExtension.php

@@ -13,9 +13,9 @@ namespace Symfony\Bundle\DebugBundle\DependencyInjection;
 
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
 use Symfony\Component\DependencyInjection\Reference;
-use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 
 /**
  * DebugExtension.

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/Bundle/TestBundle/DependencyInjection/TestExtension.php

@@ -12,7 +12,7 @@
 namespace Symfony\Bundle\FrameworkBundle\Tests\Functional\Bundle\TestBundle\DependencyInjection;
 
 use Symfony\Component\DependencyInjection\ContainerBuilder;
-use Symfony\Component\HttpKernel\DependencyInjection\Extension;
+use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Extension\PrependExtensionInterface;
 
 class TestExtension extends Extension implements PrependExtensionInterface