The anti-entropy feature has never actually worked. We've been
talking about removing it or replacing it for ages, but haven't
had a concrete motivation.
But the anti-entropy interface is the sole user of several components
of the Tx interface, and now that we're trying to replace that
interface, being able to drop those components has some appeal, so
let's remove the one thing that used them, in the hopes that this
will simplify life.
This also lets us drop ForEach and ForEachRange, which were
barely used at all. The one surviving usage (CSV export) can be
handled by using the container iterator we already have, and
making ContainerCallback exported so we can use it to just call
things for every bit.
(cherry picked from commit fff9ddc1f5)
