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: Ic4af704958819e6f65ac01be33ef5b3d69628ad0
Related: OS#4138
diff --git a/src/gprs/gtphub_main.c b/src/gprs/gtphub_main.c
index 6d470bd..f693f09 100644
--- a/src/gprs/gtphub_main.c
+++ b/src/gprs/gtphub_main.c
@@ -356,7 +356,7 @@
 
 	vty_info.copyright = gtphub_copyright;
 	vty_init(&vty_info);
-	logging_vty_add_cmds(NULL);
+	logging_vty_add_cmds();
 	osmo_talloc_vty_add_cmds();
         gtphub_vty_init(hub, cfg);