Removes defunct darksight variables and gives unathi the darksight they were supposed to have. (#22654)

Human sight:
<img width="1349" height="1349" alt="image"
src="https://github.com/user-attachments/assets/416cdd31-f27b-4b98-a900-38402f4b8279"
/>

Unathi sight:
<img width="1349" height="1349" alt="image"
src="https://github.com/user-attachments/assets/ab95c66d-a077-4c28-9d21-c24c11b2f716"
/>

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/mob/living/carbon/human/species/outsider/revenant.dm

@@ -25,7 +25,6 @@
 	default_language = LANGUAGE_REVENANT
 
 	unarmed_types = list(/datum/unarmed_attack/claws/shredding)
-	darksight = 8
 	siemens_coefficient = 0
 	rarity_value = 10
 

code/modules/mob/living/carbon/human/species/outsider/undead.dm

@@ -23,7 +23,7 @@
 	language = LANGUAGE_CULT
 	name_language = LANGUAGE_CULT
 	unarmed_types = list(/datum/unarmed_attack/claws/strong, /datum/unarmed_attack/bite/sharp)
-	darksight = 8
+	default_lighting_alpha = LIGHTING_PLANE_ALPHA_MOSTLY_INVISIBLE
 	has_organ = list() //skeletons are empty shells for now, maybe we can add something in the future
 	siemens_coefficient = 0
 	ethanol_resistance = -1 //no drunk skeletons
@@ -158,7 +158,7 @@
 	default_language = LANGUAGE_GIBBERING
 
 	unarmed_types = list(/datum/unarmed_attack/bite/infectious, /datum/unarmed_attack/claws/strong/zombie)
-	darksight = 8
+	default_lighting_alpha = LIGHTING_PLANE_ALPHA_MOSTLY_INVISIBLE
 
 	has_fine_manipulation = FALSE
 

code/modules/mob/living/carbon/human/species/species.dm

@@ -300,8 +300,6 @@
 	var/has_fine_manipulation = 1
 	/// The lower, the thicker the skin and better the insulation.
 	var/siemens_coefficient = 1
-	/// Native darksight distance.
-	var/darksight = 2
 	/// Various specific features.
 	var/flags = 0
 	/// Appearance/display related features.

code/modules/mob/living/carbon/human/species/station/monkey.dm

@@ -181,7 +181,7 @@
 	warning_low_pressure = 50
 	hazard_low_pressure = 0
 	siemens_coefficient = 0.2
-	darksight = 8
+	default_lighting_alpha = LIGHTING_PLANE_ALPHA_MOSTLY_INVISIBLE
 	death_message = "chitters faintly before crumbling to the ground, their eyes dead and lifeless..."
 	halloss_message = "crumbles to the ground, too weak to continue fighting."
 	heat_discomfort_strings = list(

code/modules/mob/living/carbon/human/species/station/slime.dm

@@ -11,7 +11,7 @@
 	flags = NO_SCAN | NO_SLIP | NO_BREATHE | NO_EMBED
 	spawn_flags = IS_RESTRICTED
 	siemens_coefficient = 3 //conductive
-	darksight = 3
+	default_lighting_alpha = LIGHTING_PLANE_ALPHA_MOSTLY_VISIBLE
 	rarity_value = 5
 	fall_mod = 0
 	grab_mod = 1.5

code/modules/mob/living/carbon/human/species/station/tajara/tajara.dm

@@ -24,7 +24,6 @@
 	maneuvers = list(
 		/singleton/maneuver/leap/tajara
 	)
-	darksight = 8
 	slowdown = -0.4
 
 	brute_mod = 1.1

code/modules/mob/living/carbon/human/species/station/unathi/unathi.dm

@@ -24,11 +24,10 @@
 		/datum/unarmed_attack/bite/sharp
 	)
 	primitive_form = SPECIES_MONKEY_UNATHI
-	darksight = 3
+	default_lighting_alpha = LIGHTING_PLANE_ALPHA_ALMOST_VISIBLE
 	gluttonous = GLUT_MESSY|GLUT_ITEM_TINY
 	stomach_capacity = 7
 	slowdown = 0.5
-
 	brute_mod = 0.8
 	fall_mod = 1.2
 	radiation_mod = 0.9 // how else did they survive nuclear armageddon?

code/modules/mob/living/carbon/human/species/station/vaurca/vaurca.dm

@@ -30,7 +30,6 @@
 	meat_type = /obj/item/reagent_containers/food/snacks/meat/bug
 	rarity_value = 4
 	slowdown = 1
-	darksight = 8 //Allows you to see through black k'ois if the night vision is on
 	eyes = "vaurca_eyes" //makes it so that eye colour is not changed when skin colour is.
 	eyes_are_impermeable = TRUE