Unused repo sync features should be dropped (per-locale repositories, svn support)
On pontoon.mozilla.org, we've recently migrated the Firefox, Thunderbird, and SeaMonkey localization repositories from hg to git. After this change, we have no projects using hg or svn as their repositories, and we have no projects using per-locale repositories (i.e. with {locale_code} in the repo URL).
We should probably drop support for these features, as they're a source of unnecessary complexity and we currently can't validate their behaviour in production. Mercurial (hg) repo support should probably be retained, as it's pretty plausibly used by some third party.
Given that I'm currently working on a sync refactor, this change is liable to be made relatively soon. If you use Pontoon with per-locale repositories or svn, now would be a Really Good Time to speak up.
Another unused sync feature that we could/should remove: having more than one target repository.
Support for more than one target repository (per-locale or otherwise) was removed in #3312.