[ospf6d] Remove 'no router' from OSPF6_NODE

Don't need command twice.
diff --git a/ospf6d/ospf6_top.c b/ospf6d/ospf6_top.c
index 5808428..b42962c 100644
--- a/ospf6d/ospf6_top.c
+++ b/ospf6d/ospf6_top.c
@@ -697,7 +697,6 @@
   install_element (OSPF6_NODE, &ospf6_router_id_cmd);
   install_element (OSPF6_NODE, &ospf6_interface_area_cmd);
   install_element (OSPF6_NODE, &no_ospf6_interface_area_cmd);
-  install_element (OSPF6_NODE, &no_router_ospf6_cmd);
 }