Remove unused logging import and LOG global var

In some modules the global LOG is not used any more. And the import
of logging is not used. This patch removes the unused logging import
and LOG vars.

Change-Id: I794ee719d76f04e70154cf67f726152fbb1ba15a

watcher/decision_engine/model/model_root.py

@@ -13,16 +13,12 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from oslo_log import log
-
 from watcher._i18n import _
 from watcher.common import exception
 from watcher.decision_engine.model import hypervisor
 from watcher.decision_engine.model import mapping
 from watcher.decision_engine.model import vm
 
-LOG = log.getLogger(__name__)
-
 
 class ModelRoot(object):
     def __init__(self):