Fixes lack of dna in old blood.

Fixes some comments about blood procs in atoms.dm
Small tweak in xeno blood blood_DNA.

code/game/objects/effects/decals/Cleanable/aliens.dm

@@ -11,7 +11,7 @@
 	icon_state = "xfloor1"
 	random_icon_states = list("xfloor1", "xfloor2", "xfloor3", "xfloor4", "xfloor5", "xfloor6", "xfloor7")
 	var/list/viruses = list()
-	blood_DNA = list()
+	blood_DNA = list("UNKNOWN DNA" = "X*")
 
 /obj/effect/decal/cleanable/xenoblood/Destroy()
 	for(var/datum/disease/D in viruses)
@@ -63,4 +63,5 @@
 
 /obj/effect/decal/cleanable/blood/xtracks
 	icon_state = "xtracks"
-	random_icon_states = null
+	random_icon_states = null
+	blood_DNA = list("UNKNOWN DNA" = "X*")

code/game/objects/effects/gibs.dm

@@ -50,11 +50,8 @@
 							gib.viruses += viruus
 							viruus.holder = gib
 
-				gib.blood_DNA = list()
 				if(MobDNA)
 					gib.blood_DNA[MobDNA.unique_enzymes] = MobDNA.blood_type
-				else if(istype(src, /obj/effect/gibspawner/xeno))
-					gib.blood_DNA["UNKNOWN DNA"] = "X*"
 				else if(istype(src, /obj/effect/gibspawner/generic)) // Probably a monkey
 					gib.blood_DNA["Non-human DNA"] = "A+"
 				var/list/directions = gibdirections[i]