Keyword router form assumed DELETE key exists.

```
  File "django/views/generic/base.py", line 86, in dispatch
    return handler(request, *args, **kwargs)
  File "go/router/view_definition.py", line 146, in post
    response = self.process_forms(request, router)
  File "go/router/view_definition.py", line 180, in process_forms
    config[key]
  = self.process_form(edit_form)
  File "go/router/view_definition.py", line 166, in process_form
    return form.to_config()
  File "go/routers/keyword/view_definition.py", line 20, in to_config
    if (not form.is_valid()) or form.cleaned_data['DELETE']:
```

We saw this error in the app multiplexer too -- we just need to copy the fix from there.