Avoid leak of the InputMapUpdater instance

[florianvazelle]

Hi, according to the Godot Documentation, when a node is creating with the new method, we need to free it from memory with the queue_free method.

Below, the commands I ran after pulling the project :

Before :

$ godot --headless --quit --verbose
Godot Engine v4.0.3.stable.official.5222a99f5 - https://godotengine.org
...
Loading resource: res://addons/EasyMenus/Nodes/menu_template_manager.tscn
Loaded builtin certs
...
ERROR: Condition "_first != nullptr" is true.
   at: ~List (./core/templates/self_list.h:106)
WARNING: ObjectDB instances leaked at exit (run with --verbose for details).
     at: cleanup (core/object/object.cpp:1982)
Leaked instance: GDScriptNativeClass:-9223138390633873009
Leaked instance: GDScript:-9222563895808359228 - Resource path: res://addons/EasyMenus/Scripts/input_map_updater.gd
Leaked instance: Node:991759488255175 - Node name: 
Hint: Leaked instances typically happen when nodes are removed from the scene tree (with `remove_child()`) but not freed (with `free()` or `queue_free()`).
ERROR: Resources still in use at exit (run with --verbose for details).
   at: clear (core/io/resource.cpp:489)
Resource still in use: res://addons/EasyMenus/Scripts/input_map_updater.gd (GDScript)
...

After :

$ godot --headless --quit --verbose
Godot Engine v4.0.3.stable.official.5222a99f5 - https://godotengine.org
...
Loading resource: res://addons/EasyMenus/Nodes/menu_template_manager.tscn
Loaded builtin certs
...