Avoid the deprecation warning for django.contrib.localflavor

On django1.5 we have the DeprecationWarning. On django1.6 the `django.contrib.localflavor` will be removed.

So, I think it's better we import `STATE_CHOICES` from the `django_localflavor_br`

```
from django_localflavor_br.br_states import STATE_CHOICES
```