fix pep8 errors

synapse/storage/__init__.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from twisted.internet import defer
-
 from synapse.storage.devices import DeviceStore
 from .appservice import (
     ApplicationServiceStore, ApplicationServiceTransactionStore
@@ -265,7 +263,6 @@ class DataStore(RoomMemberStore, RoomStore,
 
         return self.runInteraction("count_users", _count_users)
 
-
     def count_r30_users(self):
         """
         Counts the number of 30 day retained users, defined as:-