Back in May 2013 when I entered the US on an F1 Visa I had my I-94 stamped and the little card stapled to my passport. When I left again in August, they had already discontinued the form and switched to online, so they never took it back.

Unfortunately due to this, they never took that little piece of the I-94 back. When I reentered the US after those times I didn't require an I-94.

So basically now I'm stuck with an I-94 stub on my passport and have no idea what to do with it. How should I deal with this problem?