core: remove parent_id from the global event

Remove the parent_id from the global event. Remove the parent
and owner from the global object.

Use properties instead to mark parents and owners of objects.

Properties are easier to control for client exported objects and
usually a simple parent/child is not enough. For example, a client
exported node has the client as a parent but also the factory that
created the node.

src/modules/module-client-node/client-node.h

@@ -40,13 +40,11 @@ struct pw_client_node {
 	struct pw_node *node;
 
 	struct pw_resource *resource;
-	struct pw_global *parent;
 	uint32_t flags;
 };
 
 struct pw_client_node *
 pw_client_node_new(struct pw_resource *resource,
-		   struct pw_global *parent,
 		   struct pw_properties *properties,
 		   bool do_register);