Dropping Matchbox UI unless a maintainer steps up

3 months ago I made #284 (closed), indicating that Matchbox doesn't have a maintainer. It's basically unmaintained upstream, and no one in postmarketOS seem to care enough for it to step up.

After a discussion with the team, we've decided to make this issue, and if no one within a month steps up to maintain it, I'll make a MR to drop it from our repositories. If still no one steps up within a week, we'll merge it.

CC @dguthrie as you added Matchbox originally, and CC @drebrez as you upstreamed some Matchbox parts to Alpine.