can this hollow wall anchor be removed?
Yes and no. It can be removed but not without doing some damage to your drywall.

The trick is to get the nut at the rear to go back again. To do that you need to get under the front flange and be able to hold it and the screw-head together while you screw it back. 

Once it's free enough to get some sort of substantial plate behind the flange you can remove the screw almost as far as it comes and hammer it back in. It should them pull out with a little bit of persuasion.

However, since you will ultimately end up having to repair the wall anyway, it's simpler just to push it through. Use your screwdriver as a centre-punch and hammer the screwdriver till the anchor falls inside the wall. If it is really  stubborn, do not be tempted to just hit it harder. Cut or drill some small holes around it.