Resolve djcelery migration error in Vagrant

This reverts commit 368d9d74473a75844939494986ff4472d55d1ee1.

Run this like so, for most predictable results:
```
vagrant destroy
vagrant box remove kuma-ubuntu
vagrant up
```

So here's the problem:

* We have a Vagrant VM image with a partially populated database from Jan 2013
* The djcelery tables in that DB are currently in the state established by [*kuma*'s old 0001 migration](https://github.com/mozilla/kuma/blob/master/migrations/south/djcelery/0001_initial.py)
    * That is, **not** [djcelery's native 0001 migration](https://github.com/mozilla/kuma-lib/blob/master/packages/django-celery/djcelery/migrations/0001_initial.py). We started using South before djcelery did. 
    * Unfortunately, these migrations differ.
* So, attempts to apply [djcelery's own 0002 migration results in error](https://github.com/mozilla/kuma-lib/blob/master/packages/django-celery/djcelery/migrations/0002_v25_changes.py)
* Instead - at least until the Vagrant VM image is rebuilt - we need to apply [*kuma*'s old 0002 migration for djcelery](https://github.com/mozilla/kuma/blob/master/migrations/south/djcelery/0002_v25_changes.py), because it reconciles the differences.
* So, this should fix the immediate issue in Vagrant
    * A future task is to rebuild the downloadable VM image after this migrations and only *then* return full migration control to djcelery