Drop unused parameter

value_node_add() ignores it's first argument - let's drop it to make
code more compact.

Change-Id: I17c2fed4049e1c83307feda001aefc006dfbe6a3
diff --git a/src/value_node.h b/src/value_node.h
index b8183ba..84c3d7b 100644
--- a/src/value_node.h
+++ b/src/value_node.h
@@ -16,7 +16,7 @@
 	struct llist_head children;
 };
 
-struct value_node *value_node_add(void *ctx, struct value_node *parent,
+struct value_node *value_node_add(struct value_node *parent,
 				  const char *name, const char *value);
 struct value_node *value_node_find(struct value_node *parent, const char *name);
 struct value_node *value_node_find_by_idx(struct value_node *parent, int idx);