DataView\Downtime: Adjust how to handle filter columns

refs #9029

modules/monitoring/library/Monitoring/DataView/Downtime.php

@@ -8,19 +8,6 @@ namespace Icinga\Module\Monitoring\DataView;
  */
 class Downtime extends DataView
 {
-    /**
-     * {@inheritdoc}
-     */
-    public function isValidFilterTarget($column)
-    {
-        if ($column[0] === '_'
-            && preg_match('/^_(?:host|service)_/', $column)
-        ) {
-            return true;
-        }
-        return parent::isValidFilterTarget($column);
-    }
-
     /**
      * {@inheritdoc}
      */
@@ -53,7 +40,7 @@ class Downtime extends DataView
     /**
      * {@inheritdoc}
      */
-    public function getFilterColumns()
+    public function getStaticFilterColumns()
     {
         return array(
             'downtime_author',