How do I remove wobble from my DIY table?
Your table and legs and floor are turning into parallelograms.  This is because the legs have no resistance against swinging on their mounts.

I suspect that these legs are not designed to prevent this, because they expect the desk surface will be anchored in both dimensions by something else, e.g. Being attached to a wall.   

You will either need to select different legs, or find a way to brace these.  This is why most desks and chairs have some sort of cross bracing between legs, but you need more than that, or you'll just have more parallelograms.  

If it were me, I would use steel angled shelf brackets that have a nice triangle shape to them, and drill and tap appropriate machine screws into the legs, using the steel in the legs to hold the screws.  I would not drill through the hollow legs and use a bolt and nut, because all that would do is squash the hollow leg.  You would need to learn the fine art of using a hand tap, and it would also help to get centerpunches to get the pilot holes in the right place, but that is not excessively hard.  Just tedious.