Remove NotificationStatistics

NotificationStatistics was added as a spike but didn't work out as expected. This is finally removing all that unused code.
I'll drop the table in the next PR

tests/app/conftest.py

@@ -24,7 +24,6 @@ from app.models import (
     ProviderDetails,
     ProviderDetailsHistory,
     ProviderRates,
-    NotificationStatistics,
     ScheduledNotification,
     ServiceWhitelist,
     KEY_TYPE_NORMAL, KEY_TYPE_TEST, KEY_TYPE_TEAM,
@@ -840,35 +839,6 @@ def sample_provider_statistics(notify_db,
     return stats
 
 
-@pytest.fixture(scope='function')
-def sample_notification_statistics(notify_db,
-                                   notify_db_session,
-                                   service=None,
-                                   day=None,
-                                   emails_requested=2,
-                                   emails_delivered=1,
-                                   emails_failed=1,
-                                   sms_requested=2,
-                                   sms_delivered=1,
-                                   sms_failed=1):
-    if service is None:
-        service = sample_service(notify_db, notify_db_session)
-    if day is None:
-        day = date.today()
-    stats = NotificationStatistics(
-        service=service,
-        day=day,
-        emails_requested=emails_requested,
-        emails_delivered=emails_delivered,
-        emails_failed=emails_failed,
-        sms_requested=sms_requested,
-        sms_delivered=sms_delivered,
-        sms_failed=sms_failed)
-    notify_db.session.add(stats)
-    notify_db.session.commit()
-    return stats
-
-
 @pytest.fixture(scope='function')
 def mock_firetext_client(mocker, statsd_client=None):
     client = FiretextClient()