SO MANY youg-uns don't have a watch, they just check the time on their phones. So it's not even slightly surprising that they're displaying the clock in large print by default on the lock screen.
but your question... appears to require jailbreak. In the past there's been ways to "hide" a stock app, and the app you needed to hide was Clock. If you hid that, it wouldn't show the clock on the lock screen, until you rebooted your phone. Clock would reappear on one of your pages, and you'd have to hide it again. But the hiding tricks for non jailbroken phones don't seem to work for me. (probably "bugs" that got "fixed")
