Callback delete_course is deprecated. Function format_folderview_delete_course should be converted to observer of event \core\event\course_content_deleted
Moodle ver: 3.2.3+
Format_Folderview ver: 2016121300
This issue occurs when attempting to restore a previously backed up course/import content into a new course.
Following the error, call back delete_course is now deprecated so to resolve.
1. Comment out function format_folderview_delete_course in lib.php
2. Create classes/observer.php and define the right function _ course_content_deleted
3. Create db/events.php file and define callback
4. Clear cache and retry.
Ideally, I imagine developer will resolve this with next release.