Changes

Drop logging of stderr loglvel at startup

Nowadays there's far better ways to figure out logging, like checking
through VTY. For instnace, that loglevel is the general log level of the
stderr target, but says nothing about specific categories, or other log
targets, etc.
Furthermore, this way we get rid of only access to struct log_target
from libosmocore, which should be private.

Change-Id: Ibaf1bdc09ddfa0ece86da42685ced2f2504d970d