Delete unused aggregate_statistics endpoint

`@service_blueprint.route('/<uuid:service_id>/fragment/aggregate_statistics')`
is not being used anywhere, so has been removed. The `provider_statistics_dao`
can also be removed, since the function this contained was only used for
the endpoint.

app/dao/provider_statistics_dao.py

@@ -1,42 +0,0 @@
-from sqlalchemy import func
-
-from app import db
-from app.dao.date_util import get_financial_year
-from app.models import (
-    NotificationHistory,
-    SMS_TYPE,
-    EMAIL_TYPE,
-    NOTIFICATION_STATUS_TYPES_BILLABLE,
-    KEY_TYPE_TEST
-)
-
-
-def get_fragment_count(service_id, year=None):
-    shared_filters = [
-        NotificationHistory.service_id == service_id,
-        NotificationHistory.status.in_(NOTIFICATION_STATUS_TYPES_BILLABLE),
-        NotificationHistory.key_type != KEY_TYPE_TEST
-    ]
-
-    if year:
-        shared_filters.append(NotificationHistory.created_at.between(
-            *get_financial_year(year)
-        ))
-
-    sms_count = db.session.query(
-        func.sum(NotificationHistory.billable_units)
-    ).filter(
-        NotificationHistory.notification_type == SMS_TYPE,
-        *shared_filters
-    )
-
-    email_count = db.session.query(
-        func.count(NotificationHistory.id)
-    ).filter(
-        NotificationHistory.notification_type == EMAIL_TYPE,
-        *shared_filters
-    )
-    return {
-        'sms_count': int(sms_count.scalar() or 0),
-        'email_count': email_count.scalar() or 0
-    }