Nerf proc of appendicitis and viral infection

If the station event system rolls for these, there is now a 50% chance that they'll just be skipped for the round.

code/modules/events/spontaneous_appendicitis.dm

@@ -1,4 +1,7 @@
 /datum/event/spontaneous_appendicitis/start()
+	if(prob(50))
+		kill()
+		return
 	for(var/mob/living/carbon/human/H in shuffle(living_mob_list))
 		if(H.client && H.appendicitis())
 			break

code/modules/events/viral_infection.dm

@@ -4,6 +4,9 @@ var/global/list/event_viruses = list() // so that event viruses are kept around
 	var/list/viruses = list()
 
 /datum/event/viral_infection/setup()
+	if(prob(50))
+		kill()
+		return
 	announceWhen = rand(0, 3000)
 	endWhen = announceWhen + 1