Delete functions which call the job statistics tasks

The JobStatistics table is going to be deleted. There are currently
3 tasks which use the JobStatistics model via the Statistics DAO, so we
need to make sure that these tasks aren't being used before they are
deleted in a separate PR.

This commit deletes:
* The `create_initial_notification_statistic_tasks` function which gets
used to call the `record_initial_job_statistics` task.
* The `create_outcome_notification_statistic_tasks` function which gets
used to call the `record_outcome_job_statistics` task.
* And the scheduling of the `timeout-job-statistics` scheduled task.

app/config.py

@@ -231,11 +231,6 @@ class Config(object):
             'schedule': crontab(hour=4, minute=40),
             'options': {'queue': QueueNames.PERIODIC}
         },
-        'timeout-job-statistics': {
-            'task': 'timeout-job-statistics',
-            'schedule': crontab(hour=5, minute=0),
-            'options': {'queue': QueueNames.PERIODIC}
-        },
         'populate_monthly_billing': {
             'task': 'populate_monthly_billing',
             'schedule': crontab(hour=5, minute=10),