Solution for the deletion of old Database Backups for Linux SQL Server 2017 after Backups created with Ola Hallengren scripts?
I don't know if you already found a solution to your problem, but as of this moment, the extended system stored procedure xp_delete_files is supported on SQL Server 2017 when hosted on a Linux machine. 

You can edit Ola's script for database backup and remove the check when the cleanup parameter is being verified, to allow usage on a Linux machine. 

I've tried that and the removal of old backups functions just ok, as when run on Windows.