Fix tests and flake8

synapse/storage/transactions.py

@@ -14,7 +14,6 @@
 # limitations under the License.
 
 from ._base import SQLBaseStore
-from synapse.storage.engines import PostgresEngine
 from synapse.util.caches.descriptors import cached
 
 from twisted.internet import defer

tests/utils.py

@@ -53,6 +53,7 @@ def setup_test_homeserver(name="test", datastore=None, config=None, **kargs):
         config.trusted_third_party_id_servers = []
         config.room_invite_state_types = []
         config.password_providers = []
+        config.worker_replication_url = ""
 
     config.use_frozen_dicts = True
     config.database_config = {"name": "sqlite3"}