On your head they appear pressed in. I think that they're just inverted sand core plug type items. Interference fit. Perhaps a little deeper due to them wanting the cavity space available for whatever reason.
Not knowing my correctness ..but if I had to do it, I'd first drill a hole in it and attempt to insert screw (bigger one) and pull it with either a puller or heck, a claw hammer ...slide hammer. Otherwise I'd drill it as much as I could safely and collapse the thing.
That would be my Neanderthal approach.