remove usage of deprecated Role into Export

src/Bundle/ChillMainBundle/Export/ExportInterface.php

@@ -139,10 +139,8 @@ interface ExportInterface extends ExportElementInterface
 
     /**
      * Return the required Role to execute the Export.
-     *
-     * @return \Symfony\Component\Security\Core\Role\Role
      */
-    public function requiredRole();
+    public function requiredRole(): string;
 
     /**
      * Inform which ModifiersInterface (i.e. AggregatorInterface, FilterInterface)