MDL-14200 "Add group and course averages" fix for bug introduced in t…

…his patch. We are now using a seperate sql command to get the feedback text as we need to get it for the average rows too. Since it is not part of the sql to fetch attempt data we can't sort on Feedback anymore so removed the option from the table. Sorting by feedbacktext is not really useful anyway, users are more likely to want to sort by grade.

Merged from 1.9 branch.

mod/quiz/report/overview/report.php

@@ -191,6 +191,8 @@ function display($quiz, $cm, $course) {
 
             $table->column_suppress('picture');
             $table->column_suppress('fullname');
+
+            $table->no_sorting('feedbacktext');
 
             $table->column_class('picture', 'picture');
             $table->column_class('fullname', 'bold');