remove faulty code that references deleted classes or tables, fixes #4595

Closes #4595

Merge request studip/studip!3405

lib/models/Course.php

@@ -334,10 +334,7 @@ class Course extends SimpleORMap implements Range, PrivacyObject, StudipItem, Fe
 
             //Cleanup remaining wiki table entries:
             $query = 'DELETE FROM `wiki_links` WHERE `range_id` = ?';
-            $statement = DBManager::get()->execute($query, [$course->id]);
-            $query = 'DELETE FROM `wiki_locks` WHERE `range_id` = ?';
-            $statement = DBManager::get()->execute($query, [$course->id]);
-            WikiPageConfig::deleteByRange_id($course->id);
+            DBManager::get()->execute($query, [$course->id]);
 
             //Remove all entries of the course in calendars:
             $query = 'DELETE FROM `schedule_courses` WHERE `course_id` = ?';