Kill log-in-with-Facebook

```[tasklist]
### Desiderata
- [ ] Just comment it out on the login screen if that's what's expedient
- [ ] Same with Twitter while we're at it
```

![image](https://github.com/beeminder/beedroid/assets/9928/7dfc1ccf-acb6-49c3-8253-0c77ecbc6434)


## Cognata

* #158 
* #3056

_**Verbata**: oAuth, login screen, logging in via Facebook,_