Clean skippable tests that are never skipped

Author: fancyweb

Tests/Compiler/MergeExtensionConfigurationPassTest.php

@@ -12,7 +12,6 @@
 namespace Symfony\Component\DependencyInjection\Tests\Compiler;
 
 use PHPUnit\Framework\TestCase;
-use Symfony\Component\Config\Definition\BaseNode;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\Config\Resource\FileResource;
@@ -135,10 +134,6 @@ public function testThrowingExtensionsGetMergedBag()
 
     public function testReuseEnvPlaceholderGeneratedByPreviousExtension()
     {
-        if (!property_exists(BaseNode::class, 'placeholderUniquePrefixes')) {
-            $this->markTestSkipped('This test requires symfony/config ^4.4.11|^5.0.11|^5.1.3');
-        }
-
         $container = new ContainerBuilder();
         $container->registerExtension(new FooExtension());
         $container->registerExtension(new TestCccExtension());