Under iOS 10 you can "remove" stock Apple apps, like "Clock". You "delete" them just like you would any other app--hold down on the icon to get jiggly mode and the little "x" to remove it.
I used quotes above because Apple says they can still be downloaded from the App Store. Also, this
Suppport document indicates Clock is not a removable app.
Finally, hiding or removing the app still may not remove the time from the lock screen; timing is integral to many functions so it could be internal to the device rather than the app.