Allow berry to remove volatile videos

From what I understand, the current playlist mechanics do not distinguish volatile from non-volatile when it comes to removal. I think it would make sense for Berry to be able to remove volatile videos, mostly for convenience (someone given berry accidentally queues the wrong video and wants to remove it, for example). Obviously we'd not want to give berry any control over perma-queued things, but why not let Berry remove volatile videos?

(let me know if it's actually problematic, I'll see what I can do to help)