SQL recovery model for ADFS deployment
When ADFS is installed using the built-in Windows Information Database (which runs an embedded SQL Server on the AD DC), these databases are installed in SIMPLE recovery model. You could possibly take that as an indication that it would be OK to run them in SIMPLE model in your own environment, but that is up to you.

In general, if you're taking a full SQL backup daily, you should be OK discarding any historical transaction log backups prior to the full backup to save on disk space. But this depends on your need to be able to restore the database to any point in time in the past. If your policy requires you to be able to restore the database to a specific point in time, then you'll likely need to hang onto all those full, diff, and tlog backups that comprise your RPO.