Revert "Add job to keep user notifications in reasonable volume"

(Weird "Exception from line of : DateTimeZone::__construct(): Unknown or bad timezone (+00:00)"
on testwiki after this change, maybe unrelated.)

This reverts commit 20b7bb10f2ec0c547abd81be4ab09e2bb2cab3c0.

Change-Id: Ib06ac9d0ad4f0d195563a4d2cc97a1a023373996