Convert a bunch of legacy overlay calls to SSoverlays (#4015)

Bunch of overlay conversions I found in an old stash I had forgotten about.

code/game/objects/structures/electricchair.dm

@@ -6,10 +6,9 @@
 	var/obj/item/assembly/shock_kit/part = null
 	var/last_time = 1.0
 
-/obj/structure/bed/chair/e_chair/New()
-	..()
-	overlays += image('icons/obj/objects.dmi', src, "echair_over", MOB_LAYER + 1, dir)
-	return
+/obj/structure/bed/chair/e_chair/Initialize()
+	. = ..()
+	add_overlay(image('icons/obj/objects.dmi', src, "echair_over", MOB_LAYER + 1))
 
 /obj/structure/bed/chair/e_chair/attackby(obj/item/weapon/W as obj, mob/user as mob)
 	if(iswrench(W))
@@ -20,8 +19,6 @@
 		part.master = null
 		part = null
 		qdel(src)
-		return
-	return
 
 /obj/structure/bed/chair/e_chair/verb/toggle()
 	set name = "Toggle Electric Chair"
@@ -36,13 +33,6 @@
 		shock()
 		icon_state = "echair1"
 	usr << "<span class='notice'>You switch [on ? "on" : "off"] [src].</span>"
-	return
-
-/obj/structure/bed/chair/e_chair/rotate()
-	..()
-	overlays.Cut()
-	overlays += image('icons/obj/objects.dmi', src, "echair_over", MOB_LAYER + 1, dir)	//there's probably a better way of handling this, but eh. -Pete
-	return
 
 /obj/structure/bed/chair/e_chair/proc/shock()
 	if(!on)

code/game/objects/structures/watercloset.dm

@@ -179,12 +179,12 @@
 			add_fingerprint(user)
 
 /obj/machinery/shower/update_icon()	//this is terribly unreadable, but basically it makes the shower mist up
-	overlays.Cut()					//once it's been on for a while, in addition to handling the water overlay.
+	cut_overlays()					//once it's been on for a while, in addition to handling the water overlay.
 	if(mymist)
 		qdel(mymist)
 
 	if(on)
-		overlays += image('icons/obj/watercloset.dmi', src, "water", MOB_LAYER + 1, dir)
+		add_overlay(image('icons/obj/watercloset.dmi', src, "water", MOB_LAYER + 1, dir))
 		if(temperature_settings[watertemp] < T20C)
 			return //no mist for cold water
 		if(!ismist)

code/game/objects/structures/window.dm

@@ -76,13 +76,12 @@
 		updateSilicate()
 
 /obj/structure/window/proc/updateSilicate()
-	if (overlays)
-		overlays.Cut()
+	cut_overlays()
 
-	var/image/img = image(src.icon, src.icon_state)
+	var/image/img = image(icon, icon_state)
 	img.color = "#ffffff"
 	img.alpha = silicate * 255 / 100
-	overlays += img
+	add_overlay(img)
 
 /obj/structure/window/proc/shatter(var/display_message = 1)
 	playsound(src, "shatter", 70, 1)
@@ -388,7 +387,7 @@
 /obj/structure/window/update_icon()
 	//A little cludge here, since I don't know how it will work with slim windows. Most likely VERY wrong.
 	//this way it will only update full-tile ones
-	overlays.Cut()
+	cut_overlays()
 	if(!is_fulltile())
 		icon_state = "[basestate]"
 		return
@@ -403,9 +402,7 @@
 	icon_state = ""
 	for(var/i = 1 to 4)
 		var/image/I = image(icon, "[basestate][connections[i]]", dir = 1<<(i-1))
-		overlays += I
-
-	return
+		add_overlay(I)
 
 /obj/structure/window/fire_act(datum/gas_mixture/air, exposed_temperature, exposed_volume)
 	if(exposed_temperature > maximal_heat)