is it actually possible to delete modules from backpan

Sure, if your name happens to be Andreas König. The backpan is nothing more than an rsync'ed mirror of funet.fi without the --delete option active. In fact I believe that there are two public copies of backpan available. I think Andreas runs one, and I'm not sure who runs the other. Hint: if you have a machine with a couple of dozen GiB spare and reasonable, permanent connectivity, the backpan could do with another host.

The only occurrence I know of in recent memory of a module being pulled was the Time::Cubic affair of a few months ago. Only violations of some law or another have sufficient clout to get stuff pulled (and this hardly seems the case here).