mariabackup.aria_backup creates orphan Aria files

mariabackup.aria_backup test performs the following:

• create an Aria table ta
• start mariabackup
• wait till it has copied InnoDB tables, and MAD/MAI files
• execute ALTER TABLE ta ENGINE=InnoDB (this creates a new ibd file, removes MAD/MAI files and rewrites frm file)
• mariabackup copies newly created InnoDB files and frm files.

As a result, the backup will have the table in InnoDB, with ta.ibd file and ta.frm saying "InnoDB". But it additionally will have orphan ta.MAD and ta.MAI files. During restore all four files will be restored, the InnoDB table and two orphan Aria files.

The correct behavior would be to use DDL log to remove Aria files during restore (or prepare).

when it's fixed, keep_files_on_create should be changed to TRUE and marked deprecated (MDEV-23570)