Sort loot registration into respective mods (#2602)

mods/carts/init.lua

@@ -19,3 +19,10 @@ carts.path_distance_max = 3
 dofile(carts.modpath.."/functions.lua")
 dofile(carts.modpath.."/rails.lua")
 dofile(carts.modpath.."/cart_entity.lua")
+
+-- Register rails as dungeon loot
+if minetest.global_exists("dungeon_loot") then
+	dungeon_loot.register({
+		name = "carts:rail", chance = 0.35, count = {1, 6}
+	})
+end

mods/carts/mod.conf

@@ -1,3 +1,4 @@
 name = carts
 description = Carts (formerly boost_cart)
 depends = default, player_api
+optional_depends = dungeon_loot