Fixes brain surgery so it actually fixes your brain (#4061)

# About the pull request

Not using the proc to change damage? That's a paddlin'.

# Explain why it's good for the game

Bug bad

# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog

:cl: Morrow
fix: Fixes brain damage
qol: Jittering from brain damage is now capped
/:cl:

code/modules/organs/organ_internal.dm

@@ -258,7 +258,8 @@
 
 	if(organ_status >= ORGAN_BROKEN && prob(5 * delta_time))
 		owner.apply_effect(1, PARALYZE)
-		owner.make_jittery(50)
+		if(owner.jitteriness < 100)
+			owner.make_jittery(50)
 		to_chat(owner, SPAN_DANGER("Your body seizes up!"))
 
 /datum/internal_organ/brain/prosthetic //used by synthetic species

code/modules/surgery/brainrepair.dm

@@ -55,10 +55,11 @@
 
 	var/datum/internal_organ/brain/B = target.internal_organs_by_name["brain"]
 	if(B)
-		B.damage = 0
+		B.heal_damage(B.damage)
 	target.disabilities &= ~NERVOUS
 	target.sdisabilities &= ~DISABILITY_DEAF
 	target.sdisabilities &= ~DISABILITY_MUTE
+	target.jitteriness = 0
 	target.pain.recalculate_pain()
 
 	log_interact(user, target, "[key_name(user)] finished taking bone chips out of [key_name(target)]'s brain with \the [tool], finishing [surgery].")