rm unnecessary method override - it's the same as the overridden method.

questiontype.php

@@ -95,18 +95,6 @@ protected function initialise_question_instance(question_definition $question, $
 
     }
 
-    /**
-     * {@inheritdoc}
-     *
-     * @param stdClass $questiondata data defining a question, as returned by
-     *      question_bank::load_question_data().
-     * @return number|null either a fraction estimating what the student would
-     *      score by guessing, or null, if it is not possible to estimate.
-     */
-    public function get_random_guess_score($questiondata) {
-        return 0;
-    }
-
     /**
      * {@inheritdoc}
      *