explicitly join tables

from service, join organisation, the free_allowance_remainder subquery
and the ft_billing table. Being explicit reduces confusion about what
tables we're joining and how we're constraining those joins

also remove references to AnnualBilling since we've already got the
free sms allowance from the free_allowance_remainder subquery

app/dao/fact_billing_dao.py

@@ -64,11 +64,13 @@ def fetch_sms_free_allowance_remainder(start_date):
 def fetch_sms_billing_for_all_services(start_date, end_date):
 
     # ASSUMPTION: AnnualBilling has been populated for year.
-    billing_year = get_financial_year_for_datetime(start_date)
     free_allowance_remainder = fetch_sms_free_allowance_remainder(start_date).subquery()
 
     sms_billable_units = func.sum(FactBilling.billable_units * FactBilling.rate_multiplier)
-    sms_remainder = func.coalesce(free_allowance_remainder.c.sms_remainder, AnnualBilling.free_sms_fragment_limit)
+    sms_remainder = func.coalesce(
+        free_allowance_remainder.c.sms_remainder,
+        free_allowance_remainder.c.free_sms_fragment_limit
+    )
     chargeable_sms = func.greatest(sms_billable_units - sms_remainder, 0)
     sms_cost = chargeable_sms * FactBilling.rate
 
@@ -77,30 +79,30 @@ def fetch_sms_billing_for_all_services(start_date, end_date):
         Organisation.id.label('organisation_id'),
         Service.name.label("service_name"),
         FactBilling.service_id.label("service_id"),
-        AnnualBilling.free_sms_fragment_limit,
+        free_allowance_remainder.c.free_sms_fragment_limit,
         FactBilling.rate.label('sms_rate'),
         sms_remainder.label("sms_remainder"),
         sms_billable_units.label('sms_billable_units'),
         chargeable_sms.label("chargeable_billable_sms"),
         sms_cost.label('sms_cost'),
-    ).join(
-        Service.annual_billing,
+    ).select_from(
+        Service
     ).outerjoin(
         free_allowance_remainder, Service.id == free_allowance_remainder.c.service_id
     ).outerjoin(
-        Organisation, Service.organisation_id == Organisation.id
+        Service.organisation
+    ).join(
+        FactBilling, FactBilling.service_id == Service.id,
     ).filter(
-        FactBilling.service_id == Service.id,
         FactBilling.bst_date >= start_date,
         FactBilling.bst_date <= end_date,
         FactBilling.notification_type == SMS_TYPE,
-        AnnualBilling.financial_year_start == billing_year,
     ).group_by(
         Organisation.name,
         Organisation.id,
         FactBilling.service_id,
         Service.name,
-        AnnualBilling.free_sms_fragment_limit,
+        free_allowance_remainder.c.free_sms_fragment_limit,
         free_allowance_remainder.c.sms_remainder,
         FactBilling.rate,
     ).order_by(