MIxer Drumset issue

I'm pretty sure this is an issue that's been touched on in other posts, but after accidentally selecting "Drumset" in Mixer and unselecting it, i've been left with a mess of percussion notes or whatever you call them in my score and can't find a way to get rid of them. I've had to start from scratch on some scores because of this issue. Is there any way to fix this?

I've attached the file below if it's needed.