Issue #2959589 by mr.baileys, emartoni: Json data parser has unused var

src/Plugin/migrate_plus/data_parser/Json.php

@@ -15,13 +15,6 @@ use Drupal\migrate_plus\DataParserPluginBase;
  */
 class Json extends DataParserPluginBase implements ContainerFactoryPluginInterface {
 
-  /**
-   * The request headers passed to the data fetcher.
-   *
-   * @var array
-   */
-  protected $headers = [];
-
   /**
    * Iterator over the JSON data.
    *