Remove undefined param passed to {logging,osmo_stats}_vty_add_cmds

Since March 15th 2017, libosmocore API logging_vty_add_cmds() had its
parameter removed (c65c5b4ea075ef6cef11fff9442ae0b15c1d6af7). However,
definition in C file doesn't contain "(void)", which means number of
parameters is undefined and thus compiler doesn't complain. Let's remove
parameters from all callers before enforcing "(void)" on it.
API osmo_stats_vty_add_cmds never had a param list but has seem problem
(no "void"), so some users decided to pass a parameter to it.

Change-Id: I0a89586ce683ad060212355b37470c349992ec49
Related: OS#4138
diff --git a/ggsn/ggsn.c b/ggsn/ggsn.c
index 1c6bc4d..95371a2 100644
--- a/ggsn/ggsn.c
+++ b/ggsn/ggsn.c
@@ -1267,9 +1267,9 @@
 	osmo_stats_init(tall_ggsn_ctx);
 
 	vty_init(&g_vty_info);
-	logging_vty_add_cmds(NULL);
+	logging_vty_add_cmds();
 	osmo_talloc_vty_add_cmds();
-	osmo_stats_vty_add_cmds(&log_info);
+	osmo_stats_vty_add_cmds();
 	ggsn_vty_init();
 	ctrl_vty_init(tall_ggsn_ctx);