[Serializer] JsonEncoder doesn't need SerializerAware anymore

src/Symfony/Component/Serializer/Encoder/JsonEncoder.php

@@ -18,7 +18,7 @@
  *
  * @author Jordi Boggiano <j.boggiano@seld.be>
  */
-class JsonEncoder extends AbstractEncoder implements DecoderInterface
+class JsonEncoder implements EncoderInterface, DecoderInterface
 {
     /**
      * {@inheritdoc}