alerts: remove unused import in xmpp code

gracedb/alerts/xmpp.py

@@ -12,7 +12,6 @@ from django.conf import settings
 from core.time_utils import gpsToUtc
 from events.permission_utils import is_external
 from events.shortcuts import is_event
-from search.query.labels import filter_for_labels
 from superevents.shortcuts import is_superevent
 from .lvalert import send_with_lvalert_overseer, send_with_lvalert_client