Deprecate maven deploy

Set the scene for `src/build/maven-deploy.xml` aka `dists/maven/latest/build.xml`'s timely demise.

For a while now, you can just call `ant publish` to publish a build (or `ant build-opt publish` for an optimized build).

From now on, `ant nightly` also publishes, so that our jenkins set up is vastly simplified.

/cc @cunei as dbuild relies on this
/cc @huitseeker / @skyluc for the impact on uber-build

as soon as these two dependencies are removed, the duplicated maven-deploy.xml will be removed.

review by @soc please (See, I promised test.continuations.suite would be gone soon :-))