This happens because you have the iOS 10 update (or whichever version) downloaded but not installed. If you delete the update from Settings -> General -> Storage & iCloud Usage -> Manage Storage, and turn off automatic app updates so it doesn't get downloaded again, the prompts go away.

Worked for me on iOS 9.3.5 after another HN user recommended it, anyway. Older versions I'm not sure about, but it can't hurt to try.