Remove the `rust` tool

[brson]

As discussed, it has a lot of problems, no owner, we can't commit to fixing it for Rust 1.0.

[brson]

Nominating.

[catamorphism]

I'm going to do it.

[catamorphism]

Done -- I'm just running a second round of tests after doing a clean build to make sure nothing is left behind, and then I'll submit a PR.