makes w_class use defines (#9848)

code/modules/hydroponics/grown_inedible.dm

@@ -41,7 +41,7 @@
 	icon = 'icons/obj/trash.dmi'
 	icon_state = "corncob"
 	item_state = "corncob"
-	w_class = 2.0
+	w_class = ITEMSIZE_SMALL
 	throwforce = 0
 	throw_speed = 4
 	throw_range = 20
@@ -64,7 +64,7 @@
 		)
 	icon_state = "banana_peel"
 	item_state = "banana_peel"
-	w_class = 2.0
+	w_class = ITEMSIZE_SMALL
 	throwforce = 0
 	throw_speed = 4
 	throw_range = 20

code/modules/hydroponics/seed_machines.dm

@@ -3,7 +3,7 @@
 	desc = "A small disk used for carrying data on plant genetics."
 	icon = 'icons/obj/hydroponics_machines.dmi'
 	icon_state = "disk"
-	w_class = 1.0
+	w_class = ITEMSIZE_TINY
 
 	var/list/genes = list()
 	var/genesource = "unknown"

code/modules/hydroponics/seed_packets.dm

@@ -5,7 +5,7 @@ var/global/list/plant_seed_sprites = list()
 	name = "packet of seeds"
 	icon = 'icons/obj/seeds.dmi'
 	icon_state = "blank"
-	w_class = 2.0
+	w_class = ITEMSIZE_SMALL
 
 	var/seed_type
 	var/datum/seed/seed

code/modules/hydroponics/trays/tray_reagents.dm

@@ -5,7 +5,7 @@
 	flags = NOBLUDGEON
 	slot_flags = SLOT_BELT
 	throwforce = 4
-	w_class = 2.0
+	w_class = ITEMSIZE_SMALL
 	throw_speed = 2
 	throw_range = 10
 	var/toxicity = 4
@@ -91,7 +91,7 @@
 	icon_state = "bottle16"
 	flags = OPENCONTAINER
 	possible_transfer_amounts = null
-	w_class = 2.0
+	w_class = ITEMSIZE_SMALL
 
 	//Like a shot glass!
 	amount_per_transfer_from_this = 10