Reduces the number of skulls spawned by crystal legion by 1 (#3117)

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## About The Pull Request

Here, catch.

![image](https://github.com/shiptest-ss13/Shiptest/assets/24857008/bd6ab17a-383e-4555-93de-ad55253e94e5)


## Why It's Good For The Game

Reduces the capacity for crystal legion to instakill people by shitting
out 2 skulls which immediately fly over to people and shit out shrapnel
when killed. It's like a mine but it chases you. If you can't get to a
safe distance the pattern almost guarantees getting hit twice.

## Changelog

:cl:
balance: crystal legion spawn 1 less skull per spawn wave, now 1 (like
normal legion)
/:cl:

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Signed-off-by: Theos <[email protected]>

code/modules/mob/living/simple_animal/hostile/mining_mobs/hivelord.dm

@@ -355,7 +355,6 @@
 	icon_living = "disfigured_legion"
 	icon_aggro = "disfigured_legion"
 	icon_dead = "disfigured_legion"
-	difficulty = 2
 	brood_type = /mob/living/simple_animal/hostile/asteroid/hivelordbrood/legion/crystal
 	loot = list(/obj/item/organ/regenerative_core/legion/crystal)