remove redundant ExampleConfig
remove redundant ExampleConfig

This fixes the test error:

```
django.core.exceptions.ImproperlyConfigured: Cannot import 'example'.
Check that 'tests.apps.example.apps.ExampleConfig.name' is correct.
```

pydanny/dj-stripe,pydanny/dj-stripe,dj-stripe/dj-stripe,dj-stripe/dj-stripe