Remove uses of logger name "oslo_messaging"

The old olso namespace package logger config should not be used as
stated by [1], this patch removes the redundant one.

[1] https://github.com/openstack/oslo.log/blob/master/oslo_log/log.py#L466

Change-Id: I58401867cfe34b1becd438702888e3875602b38d

ironic/conf/opts.py

@@ -88,9 +88,6 @@ def update_opt_defaults():
             'amqp=WARNING',
             'amqplib=WARNING',
             'qpid.messaging=INFO',
-            # TODO(therve): when bug #1685148 is fixed in oslo.messaging, we
-            # should be able to remove one of those 2 lines.
-            'oslo_messaging=INFO',
             'oslo.messaging=INFO',
             'sqlalchemy=WARNING',
             'stevedore=INFO',