Revert "Remove unused import"

This reverts commit ab37bef83b.

synapse/storage/push_rule.py

@@ -16,6 +16,7 @@
 from ._base import SQLBaseStore
 from synapse.util.caches.descriptors import cachedInlineCallbacks, cachedList
 from synapse.push.baserules import list_with_base_rules
+from synapse.api.constants import EventTypes
 from twisted.internet import defer
 
 import logging