Fix remove iv needing power to operate. (#4070)

# About the pull request
fixes: #3848
and add a skill check like for the blood pack.
also turned four variable with a single letter into better ones.

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# Explain why it's good for the game
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

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# Changelog
:cl:
add: Add a skill check to operate IV.
fix: Fix remove iv needing power to operate.
/:cl:

---------

Co-authored-by: Julien <[email protected]>
Co-authored-by: forest2001 <[email protected]>
Co-authored-by: Drathek <[email protected]>

code/game/machinery/iv_drip.dm

@@ -11,6 +11,8 @@
 	var/mode = 1 // 1 is injecting, 0 is taking blood.
 	var/obj/item/reagent_container/beaker = null
 	var/datum/beam/current_beam
+	//make it so that IV doesn't require power to function.
+	use_power = USE_POWER_NONE
 
 /obj/structure/machinery/iv_drip/update_icon()
 	if(attached)
@@ -44,33 +46,25 @@
 	else if(!QDELETED(src) && attached)
 		current_beam = beam(attached, "iv_tube")
 
-/obj/structure/machinery/iv_drip/power_change()
-	. = ..()
-	if(stat & NOPOWER && attached)
-		visible_message("\The [src] retracts its IV tube and shuts down.")
-		attached.active_transfusions -= src
-		attached = null
-		update_beam()
-		update_icon()
-
 /obj/structure/machinery/iv_drip/Destroy()
 	attached?.active_transfusions -= src
 	update_beam()
 	. = ..()
 
 /obj/structure/machinery/iv_drip/MouseDrop(over_object, src_location, over_location)
 	..()
-	if(inoperable())
-		visible_message("\The [src] is not powered.")
-		return
 
 	if(ishuman(usr))
-		var/mob/living/carbon/human/H = usr
-		if(H.stat || get_dist(H, src) > 1 || H.blinded || H.lying)
+		var/mob/living/carbon/human/user = usr
+		if(user.stat || get_dist(user, src) > 1 || user.blinded || user.lying)
+			return
+
+		if(!skillcheck(user, SKILL_SURGERY, SKILL_SURGERY_NOVICE))
+			to_chat(user, SPAN_WARNING("You don't know how to [attached ? "disconnect" : "connect"] this!"))
 			return
 
 		if(attached)
-			H.visible_message("[H] detaches \the [src] from \the [attached].", \
+			user.visible_message("[user] detaches \the [src] from \the [attached].", \
 			"You detach \the [src] from \the [attached].")
 			attached.active_transfusions -= src
 			attached = null
@@ -80,35 +74,35 @@
 			return
 
 		if(in_range(src, usr) && iscarbon(over_object) && get_dist(over_object, src) <= 1)
-			H.visible_message("[H] attaches \the [src] to \the [over_object].", \
+			user.visible_message("[user] attaches \the [src] to \the [over_object].", \
 			"You attach \the [src] to \the [over_object].")
 			attached = over_object
 			attached.active_transfusions += src
 			update_beam()
 			update_icon()
 			start_processing()
 
-
-/obj/structure/machinery/iv_drip/attackby(obj/item/W, mob/living/user)
-	if (istype(W, /obj/item/reagent_container))
+/obj/structure/machinery/iv_drip/attackby(obj/item/container, mob/living/user)
+	if (istype(container, /obj/item/reagent_container))
 		if(beaker)
 			to_chat(user, SPAN_WARNING("There is already a reagent container loaded!"))
 			return
 
-		if((!istype(W, /obj/item/reagent_container/blood) && !istype(W, /obj/item/reagent_container/glass)) || istype(W, /obj/item/reagent_container/glass/bucket))
+		if((!istype(container, /obj/item/reagent_container/blood) && !istype(container, /obj/item/reagent_container/glass)) || istype(container, /obj/item/reagent_container/glass/bucket))
 			to_chat(user, SPAN_WARNING("That won't fit!"))
 			return
 
-		if(user.drop_inv_item_to_loc(W, src))
-			beaker = W
+		if(user.drop_inv_item_to_loc(container, src))
+			beaker = container
 
 			var/reagentnames = ""
-			for(var/datum/reagent/R in beaker.reagents.reagent_list)
-				reagentnames += ";[R.name]"
+
+			for(var/datum/reagent/chem in beaker.reagents.reagent_list)
+				reagentnames += ";[chem.name]"
 
 			log_admin("[key_name(user)] put a [beaker] into [src], containing [reagentnames] at ([src.loc.x],[src.loc.y],[src.loc.z]).")
 
-			to_chat(user, "You attach \the [W] to \the [src].")
+			to_chat(user, "You attach \the [container] to \the [src].")
 			update_beam()
 			update_icon()
 		return
@@ -151,20 +145,20 @@
 				if(prob(5)) visible_message("\The [src] pings.")
 				return
 
-			var/mob/living/carbon/T = attached
+			var/mob/living/carbon/patient = attached
 
-			if(!istype(T))
+			if(!istype(patient))
 				return
-			if(ishuman(T))
-				var/mob/living/carbon/human/H = T
-				if(H.species && H.species.flags & NO_BLOOD)
+			if(ishuman(patient))
+				var/mob/living/carbon/human/human_patient = patient
+				if(human_patient.species && human_patient.species.flags & NO_BLOOD)
 					return
 
 			// If the human is losing too much blood, beep.
-			if(T.blood_volume < BLOOD_VOLUME_SAFE) if(prob(5))
+			if(patient.blood_volume < BLOOD_VOLUME_SAFE) if(prob(5))
 				visible_message("\The [src] beeps loudly.")
 
-			T.take_blood(beaker,amount)
+			patient.take_blood(beaker,amount)
 			update_icon()
 
 /obj/structure/machinery/iv_drip/attack_hand(mob/user as mob)