Removes xenomorphs (#6686)

Xenomorphs are pretty much badly done and don't really fit at all. This pr fully removes the human type ones, alongside with the infection, eggs and facehuggers.

code/datums/diseases/xeno_transformation.dm

@@ -1,64 +0,0 @@
-//Xenomicrobes
-
-/datum/disease/xeno_transformation
-	name = "Xenomorph Transformation"
-	max_stages = 5
-	spread = "Syringe"
-	spread_type = SPECIAL
-	cure = "Spaceacillin & Glycerol"
-	cure_id = list("spaceacillin", "glycerol")
-	cure_chance = 5
-	agent = "Rip-LEY Alien Microbes"
-	affected_species = list("Human")
-	var/gibbed = 0
-
-/datum/disease/xeno_transformation/stage_act()
-	..()
-	switch(stage)
-		if(2)
-			if (prob(8))
-				to_chat(affected_mob, "<span class='warning'>Your throat feels scratchy.</span>")
-				affected_mob.take_organ_damage(1)
-			if (prob(9))
-				to_chat(affected_mob, "<span class='warning'>Kill...</span>")
-			if (prob(9))
-				to_chat(affected_mob, "<span class='warning'>Kill...</span>")
-		if(3)
-			if (prob(8))
-				to_chat(affected_mob, "<span class='warning'>Your throat feels very scratchy.</span>")
-				affected_mob.take_organ_damage(1)
-			/*
-			if (prob(8))
-				affected_mob.say(pick("Beep, boop", "beep, beep!", "Boop...bop"))
-			*/
-			if (prob(10))
-				to_chat(affected_mob, "<span class='warning'>Your skin feels tight.</span>")
-				affected_mob.take_organ_damage(5)
-			if (prob(4))
-				to_chat(affected_mob, "<span class='warning'>You feel a stabbing pain in your head.</span>")
-				affected_mob.Paralyse(2)
-			if (prob(4))
-				to_chat(affected_mob, "<span class='warning'>You can feel something move...inside.</span>")
-		if(4)
-			if (prob(10))
-				to_chat(affected_mob, pick("<span class='warning'>Your skin feels very tight.</span>", "<span class='warning'>Your blood boils!</span>"))
-				affected_mob.take_organ_damage(8)
-			if (prob(20))
-				affected_mob.say(pick("You look delicious.", "Going to... devour you...", "Hsssshhhhh!"))
-			if (prob(8))
-				to_chat(affected_mob, "<span class='warning'>You can feel... something...inside you.</span>")
-		if(5)
-			to_chat(affected_mob, "<span class='warning'>Your skin feels impossibly calloused...</span>")
-			affected_mob.adjustToxLoss(10)
-			affected_mob.updatehealth()
-			if(prob(40))
-				if(gibbed != 0) return 0
-				src.cure(0)
-				gibbed = 1
-				var/mob/living/carbon/human/H = affected_mob
-				if(istype(H))
-					var/turf/origin = find_loc(affected_mob)
-					gibs(origin)
-					H.set_species("Xenomorph [pick(list("Hunter","Sentinel","Drone"))]")
-					return
-				affected_mob.gib()