Make sure to erase signs, if creator removes them.

This works without needing to depend on `signs` here since
we call the embedded on_destruct. We leave other on_destruct
calls alone for now since we may want to retain the current
behavior where no triggers happen if you use this method of
replacing nodes in a puzzle, which is needed for several
puzzles I've made so far.

mods/mech/init.lua

@@ -1053,6 +1053,12 @@ minetest.register_node("mech:node_creator", {
 			return
 		end
 
+		-- if erasing signs, we have to remove entities
+		local d2 = minetest.registered_nodes[minetest.get_node(p2).name]
+		if d2.groups and d2.groups.sign then
+			d2.on_destruct(p2)
+		end
+
 		local n2 = minetest.deserialize(meta:get_string("node"))
 		minetest.swap_node(p2, n2)
 

mods/signs/init.lua

@@ -122,7 +122,7 @@ minetest.register_node("signs:sign", {
 	inventory_image = "sign.png",
 	walkable = false,
 	tiles = {"itb_blank.png"},
-	groups = { node = 1 },
+	groups = { node = 1, sign = 1 },
 	node_box = {
 		type = "fixed",
 		fixed = {
@@ -211,7 +211,7 @@ minetest.register_node("signs:sign_wall", {
 	inventory_image = "sign.png",
 	walkable = false,
 	tiles = {"sign.png"},
-	groups = { node = 1 },
+	groups = { node = 1, sign = 1 },
 	selection_box = {
 		type = "fixed",
 		fixed = {