Fix bug where demo tokens are not created

[charleshan]

It looks like these lines are preventing the creation of new tokens with predefined keys so the current implementation doesn't work with existing users. This pull request simply removes those lines.

django-rest-framework-passwordless/drfpasswordless/utils.py

Lines 43 to 53 in 0a382e9

	token = CallbackToken.objects.filter(user=user).first()
	if token:
	return token
	else:
	return CallbackToken.objects.create(
	user=user,
	key=api_settings.PASSWORDLESS_DEMO_USERS[user.pk],
	to_alias_type=alias_type_u,
	to_alias=getattr(user, to_alias_field),
	type=token_type
	)

[aaronn]

I don't think this is the way to go: you'd be creating a new callback token every time the user logs in.