Since ce9fec3e896571835ac5bfd2980d6836f2b29f0d libosmocore ignores
parameters to log_vty_command_* functions. Hence parameter of
logging_vty_add_cmds() is ignored too. As we depend on much later
libosmocore version anyway, we can simplify code somewhat by removing
parameters which will be ignored anyway.
Change-Id: I62f752fd88f1d8fefa563648f9864c7c31f87991