[NO GBP] Fix parasitic infection to cure upon liver removal (#77297)

## About The Pull Request

Fixes #77275

In #76766 I had reworked diseases and organs to have optional required
organs. The parasitic infection disease required livers, but it only
skipped the harmful effects from processing instead of curing the
disease like it should have.

I have to be careful doing this to advanced diseases since they can have
multiple symptoms, so sypmtoms are considered neutered if the required
organ isn't present. Regular diseases however don't have multiple
symptoms and should be cured.

Also the parastic infection is a non contagious disease, so upon the
liver being removed, the disease is cured from both the person and the
organ itself.

## Why It's Good For The Game

One more bug destroyed.


## Changelog

🆑
fix: Fix parasitic infection to cure upon liver removal
/🆑

code/datums/diseases/_disease.dm

@@ -70,6 +70,7 @@
 
 	if(required_organ)
 		if(!has_required_infectious_organ(affected_mob, required_organ))
+			cure()
 			return FALSE
 
 	if(has_cure())

code/datums/diseases/parasitic_infection.dm

@@ -19,12 +19,6 @@
 	if(!.)
 		return
 
-	var/obj/item/organ/internal/liver/affected_liver = affected_mob.get_organ_by_type(/obj/item/organ/internal/liver)
-	if(!affected_liver)
-		affected_mob.visible_message(span_notice("<B>[affected_mob]'s liver is covered in tiny larva! They quickly shrivel and die after being exposed to the open air.</B>"))
-		cure()
-		return FALSE
-
 	switch(stage)
 		if(1)
 			if(SPT_PROB(2.5, seconds_per_tick))
@@ -48,6 +42,8 @@
 				else
 					to_chat(affected_mob, span_warning("You feel much, MUCH lighter!"))
 					affected_mob.vomit(20, TRUE)
+					// disease code already checks if the liver exists otherwise it is cured
+					var/obj/item/organ/internal/liver/affected_liver = affected_mob.get_organ_slot(ORGAN_SLOT_LIVER)
 					affected_liver.Remove(affected_mob)
 					affected_liver.forceMove(get_turf(affected_mob))
 					cure()