Disable sending activation email also when doing external_auth and setti...

...ng BYPASS_ACTIVATION_EMAIL_FOR_EXTAUTH=True


Sorry for this....it was a previous PR with some discussions, but wrong branch and I was forced to clean my master branch
I would suggest this spacing is weird; I had to reread it a few times before I realized the second `not` was outside a conjunction. Perhaps
```python
send_email = (
    not settings.FEATURES.get('AUTOMATIC_AUTH_FOR_TESTING') and
    not (settings.FEATURES.get('BYPASS_ACTIVATION_EMAIL_FOR_EXTAUTH') and DoExternalAuth)
)
```