Removed dead code and various cleaning

Author: saro0h

Definition/Dumper/XmlReferenceDumper.php

@@ -59,7 +59,7 @@ private function writeNode(NodeInterface $node, $depth = 0, $root = false, $name
             });
 
             if (count($remapping)) {
-                list($singular, $plural) = current($remapping);
+                list($singular) = current($remapping);
                 $rootName = $singular;
             }
         }

Definition/Dumper/YamlReferenceDumper.php

@@ -14,7 +14,6 @@
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\Config\Definition\NodeInterface;
 use Symfony\Component\Config\Definition\ArrayNode;
-use Symfony\Component\Config\Definition\ScalarNode;
 use Symfony\Component\Config\Definition\EnumNode;
 use Symfony\Component\Config\Definition\PrototypedArrayNode;
 use Symfony\Component\Yaml\Inline;