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/service/rest.py

@@ -65,7 +65,6 @@ from app.dao.service_letter_contact_dao import (
     add_letter_contact_for_service,
     update_letter_contact
 )
-from app.dao.provider_statistics_dao import get_fragment_count
 from app.dao.users_dao import get_user_by_id
 from app.errors import (
     InvalidRequest,
@@ -299,17 +298,6 @@ def remove_user_from_service(service_id, user_id):
     return jsonify({}), 204
 
 
-@service_blueprint.route('/<uuid:service_id>/fragment/aggregate_statistics')
-def get_service_provider_aggregate_statistics(service_id):
-    year = request.args.get('year')
-    if year is not None:
-        try:
-            year = int(year)
-        except ValueError:
-            raise InvalidRequest('Year must be a number', status_code=400)
-    return jsonify(data=get_fragment_count(service_id, year=year))
-
-
 # This is placeholder get method until more thought
 # goes into how we want to fetch and view various items in history
 # tables. This is so product owner can pass stories as done