[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

jupyterhub/app.py

@@ -72,7 +72,6 @@ from .log import CoroutineLogFormatter, log_request
 from .metrics import (
     HUB_STARTUP_DURATION_SECONDS,
     INIT_SPAWNERS_DURATION_SECONDS,
-    MONTHLY_ACTIVE_USERS,
     RUNNING_SERVERS,
     TOTAL_USERS,
     PeriodicMetricsCollector,

jupyterhub/metrics.py

@@ -23,7 +23,7 @@ from datetime import datetime, timedelta
 from enum import Enum
 
 from prometheus_client import Gauge, Histogram
-from tornado.ioloop import IOLoop, PeriodicCallback
+from tornado.ioloop import PeriodicCallback
 from traitlets import Any, Bool, Integer
 from traitlets.config import LoggingConfigurable