DoH is visible on Android

Currently, we forcefully disable DoH on desktop.

We didn't do on Android because it wasn't visible, but now it is, and its descriptions are not coherent with out threat model at all.

(Notice: I'm not against DoH, we have a couple of open issues; generally speaking it doesn't feel good to use a single provider which will see at least all the DNS traffic you do in the browser, but it might be more complicated than this).

In addition to hiding the UI, we'll need to set disabled as the default setting. I don't know which layer we'll need to do it at.