Some Mob Define Cleanup (#22536)

Just removing a few ancient 2008-era vars that were on every mob
globally, but were completely unused in the modern code. I thought about
removing the Mutations too, but since the Hulk mutation is actually used
by a tiny handful of things, I would probably have to do that in a
separate PR by turning the Hulk code into an Element instead.

code/modules/mob/death.dm

@@ -18,7 +18,7 @@
 	flick(anim, animation)
 
 	if(do_gibs)
-		gibs(loc, viruses, dna, get_gibs_type())
+		gibs(loc, dna, get_gibs_type())
 
 	QDEL_IN(animation, 15)
 	QDEL_IN(src, 15)