You can go through iCloud settings and delete all backups then sign out of iCloud.
You probably know this. And, you might suspect as I do that nothing is ever really deleted, they just disable your access to it and don't do anymore backups. There's nothing we can do about that, we gave it to them, they'll keep it forever, associated with your account, no matter what they say--at least that's what I think. Maybe Apple really does delete it, but I doubt it.
Google doesn't delete anything, I doubt Apple does, either: