Cleanup remaining EditorUndoRedoManager usages

editor/plugins/skeleton_3d_editor_plugin.h

@@ -41,7 +41,6 @@
 #include "scene/resources/immediate_mesh.h"
 
 class EditorInspectorPluginSkeleton;
-class EditorUndoRedoManager;
 class Joint;
 class PhysicalBone3D;
 class Skeleton3DEditorPlugin;
@@ -65,8 +64,6 @@ class BoneTransformEditor : public VBoxContainer {
 	Skeleton3D *skeleton = nullptr;
 	// String property;
 
-	Ref<EditorUndoRedoManager> undo_redo;
-
 	bool toggle_enabled = false;
 	bool updating = false;