Sort loot registration into respective mods (#2602)

mods/vessels/init.lua

@@ -228,3 +228,10 @@ minetest.register_craft({
 	recipe = "vessels:shelf",
 	burntime = 30,
 })
+
+-- Register glass fragments as dungeon loot
+if minetest.global_exists("dungeon_loot") then
+	dungeon_loot.register({
+		name = "vessels:glass_fragments", chance = 0.35, count = {1, 4}
+	})
+end

mods/vessels/mod.conf

@@ -1,3 +1,4 @@
 name = vessels
 description = Minetest Game mod: vessels
 depends = default
+optional_depends = dungeon_loot