Author: Mikhail Golenkov
MDL-71044 backup: backup_cleanup_task task to remove old files
http://git.moodle.org/gw?p=moodle.git;a=commit;h=68588a8f477046f744e7a736e4652c5917a71c64
http://github.com/moodle/moodle/commit/68588a8f477046f744e7a736e4652c5917a71c64
+ 3.11 en [taskbackupcleanup,core_admin]