Remove everything for the performance platform

We no longer will send them any stats so therefore don't need the code
- the code to work out the nightly stats
- the performance platform client
- any configuration for the client
- any nightly tasks that kick off the sending off the stats

We will require a change in cronitor as we no longer will have this task
run meaning we need to delete the cronitor check.

app/dao/fact_notification_status_dao.py

@@ -430,18 +430,6 @@ def fetch_monthly_template_usage_for_service(start_date, end_date, service_id):
     return query.all()
 
 
-def get_total_sent_notifications_for_day_and_type(day, notification_type):
-    result = db.session.query(
-        func.sum(FactNotificationStatus.notification_count).label('count')
-    ).filter(
-        FactNotificationStatus.notification_type == notification_type,
-        FactNotificationStatus.key_type != KEY_TYPE_TEST,
-        FactNotificationStatus.bst_date == day,
-    ).scalar()
-
-    return result or 0
-
-
 def get_total_notifications_for_date_range(start_date, end_date):
     query = db.session.query(
         FactNotificationStatus.bst_date.cast(db.Text).label("bst_date"),

app/dao/notifications_dao.py

@@ -684,8 +684,11 @@ def dao_get_notifications_by_references(references):
     ).all()
 
 
-def dao_get_total_notifications_sent_per_day_for_performance_platform(start_date, end_date):
+def dao_get_notifications_processing_time_stats(start_date, end_date):
     """
+    For a given time range, returns the number of notifications sent and the number of
+    those notifications that we processed within 10 seconds
+
     SELECT
     count(notifications),
     coalesce(sum(CASE WHEN sent_at - created_at <= interval '10 seconds' THEN 1 ELSE 0 END), 0)