General fix to update tint applying/removing blindness, tweak to facehuggers. (#26513)

* Removes the blindness from Facehuggers and ties it to `update_tint()`.
`update_tint()` now properly removes and adds blindness.

* Removes unneeded overlay.

code/modules/mob/living/carbon/alien/special/facehugger.dm

@@ -141,7 +141,6 @@
 		target.equip_to_slot_if_possible(src, SLOT_HUD_WEAR_MASK, FALSE, TRUE)
 		if(!sterile)
 			M.KnockDown(impregnation_time + 2 SECONDS)
-			M.EyeBlind(impregnation_time + 2 SECONDS)
 			flags |= NODROP //You can't take it off until it dies... or figures out you're an IPC.
 
 	GoIdle() //so it doesn't jump the people that tear it off

code/modules/mob/living/carbon/carbon_procs.dm

@@ -1201,14 +1201,13 @@ so that different stomachs can handle things in different ways VB*/
 /mob/living/carbon/proc/update_tint()
 	var/tinttotal = get_total_tint()
 	if(tinttotal >= TINT_BLIND)
-		overlay_fullscreen("tint", /atom/movable/screen/fullscreen/stretch/blind)
-		ADD_TRAIT(src, TRAIT_BLIND, "tint")
+		become_blind("tint")
 	else if(tinttotal >= TINT_IMPAIR)
 		overlay_fullscreen("tint", /atom/movable/screen/fullscreen/stretch/impaired, 2)
-		REMOVE_TRAIT(src, TRAIT_BLIND, "tint")
+		cure_blind("tint")
 	else
 		clear_fullscreen("tint", 0)
-		REMOVE_TRAIT(src, TRAIT_BLIND, "tint")
+		cure_blind("tint")
 
 /mob/living/carbon/proc/get_total_tint()
 	. = 0