remove broken call to parent constructor

CRM/Event/Import/Parser/Participant.php

@@ -65,7 +65,6 @@ class CRM_Event_Import_Parser_Participant extends CRM_Import_Parser {
    * @param array $mapperKeys
    */
   public function __construct(&$mapperKeys = []) {
-    parent::__construct();
     $this->_mapperKeys = &$mapperKeys;
   }