You have only added Photos twice to the home screen, the app has not been duplicated. You can drag the icon of an app directly from the App Library to as many different pages of the home screen you want. And once you have multiple instances on your home screen, you even combine them on the same page of the home screen.
You can remove the duplicate Photos icons from the Home Screen by tapping it and holding down on it until it wiggles, then click the "-" on the icon of the app. The app will only be uninstalled, if you remove the last icon as well.