You don't need to delete flashback logs. Oracle will automatically handle the deletion of flashback logs.
Configure the retention policy to delete archive logs older than a particular time.
Configure the archivelog deletion policy to manage deletion of logs that have been applied to the standby.
CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 7 DAYS;
CONFIGURE ARCHIVELOG DELETION POLICY TO APPLIED ON STANDBY;
In the worst case if you find out you need archivelogs which have been deleted from disk then you can restore them as they have already been backed up by RMAN.