Weblate can't catch up automatically to the monorepository merge

[cfm]

Weblate is smartly declining to fast-forward the securedrop/securedrop-client component with 522 incoming commits from this repository. I replicated this scenario on weblate-sandbox and found that:

1. Weblate's outgoing commits now have conflicts, because they still update files under securedrop_client/locale, which now lives at client/securedrop_client/locale.
2. We can update these paths, but then the incoming merge may conflict. (It did on weblate-sandbox, anyway, because it had a different head to begin with; let's not risk it on weblate.)
3. We can reset Weblate from Git, but then we lose all the pending translations in Weblate's outgoing commits.

I've sketched the necessary intervention in #1742, which I'll pick up on Monday with a snapshot of weblate's database and filesystem for safety's sake.

[cfm]

If I'm right about this, we would have had to do more or less the same thing before the monorepository merge. So no harm done here: just six of one, half a dozen of another.