It in my iPad.Except it shows all the time, of course. I certainly don't allow "Hey Siri" on my device, and there's the slider for Siri in "Allow Access When Locked", right where it's supposed to be. Toggling it on doesn't enable "Hey Siri", either.
On the 7 and later, you don't (supposedly) have to be plugged into power to use "Hey Siri", but that shouldn't change where and when the option(s) show up in the UI.