gdbus: Remove root node 'name' attribute in introspection

generate_introspection_xml generates the root <node> tags with a
'name' attribute. This seems to be a valid attribute but it is not
consistent with the way the D-Bus daemon generates empty nodes.

For example if we register "/foo/bar", D-Bus daemon will generate for
"/foo" a introspection which looks like this:

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
  <node name="bar"/>

and generate_introspection_xml generates for "/foo/bar":

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
<node name="/foo/bar">

Just don't add the 'name' attribute to the root node.  The GLib
binding for D-Bus does it the same way.
diff --git a/gdbus/object.c b/gdbus/object.c
index 49006ec..eaa2e1a 100644
--- a/gdbus/object.c
+++ b/gdbus/object.c
@@ -162,7 +162,7 @@
 	gstr = g_string_new(DBUS_INTROSPECT_1_0_XML_DOCTYPE_DECL_NODE);
-	g_string_append_printf(gstr, "<node name=\"%s\">\n", path);
+	g_string_append_printf(gstr, "<node>\n");
 	for (list = data->interfaces; list; list = list->next) {
 		struct interface_data *iface = list->data;