Changes

Drop use of deprecated vty is_config_node() cb

This callback was drepecated and is not ever called since
libosmocore.git 70ce871532ab21955e0955d7e230eae65438f047 (release 1.3.0).

See also libosmocore.git d31de237582f6fe3315d61bb9a488d4cda92654e.

Change-Id: Ifdecb35f329c243222bc5d77f0a6d394c9413684