MDL-27626 moodle1_qtype_handler::process_question() is not supposed to return anything

Returning the converted array has no benefit here and makes the things
more complicated. From now on, the method is supposed to write what it
needs directly into the opened file, without returning anything.

backup/converter/moodle1/handlerlib.php

@@ -1147,14 +1147,12 @@ class moodle1_question_bank_handler extends moodle1_xml_handler {
             } else {
                 $this->xmlwriter->begin_tag('plugin_qtype_'.$qtype.'_question');
                 $handler->use_xml_writer($this->xmlwriter);
-                $data = array_merge($data, $handler->process_question($data, $raw));
+                $handler->process_question($data, $raw);
                 $this->xmlwriter->end_tag('plugin_qtype_'.$qtype.'_question');
             }
         }
 
         $this->xmlwriter->end_tag('question');
-
-        return $data;
     }
 
     /**
@@ -1287,10 +1285,8 @@ abstract class moodle1_qtype_handler extends moodle1_plugin_handler {
      *
      * @param array $data grouped question data
      * @param array $raw grouped raw QUESTION data
-     * @return array converted data
      */
     public function process_question(array $data, array $raw) {
-        return $data;
     }
 
     /// implementation details follow //////////////////////////////////////////