Simplify vampire blood-bottling

Now moved to (c), rather than being on the ability menu; vampires
will bottle anything they can bottle, butcher anything that has a
hide but can't be butchered, and give up otherwise.

This is a small buff (since they can now bottle blood from level 1
rather than needing to wait for xl 6), but also a small nerf,
since they can no longer turn poisonous corpses into skeletons to
weaken enemy necromancers in advance. I deem it a net draw.