deprecate (and remove) now-unused parts of bashbrew, like "bashbrew build"

[tianon]

With meta-scripts now doing all our builds, there's a lot of functionality in bashbrew that no longer needs to exist.

[tianon]

An important part of this is getting rid of manifest-tool, which we probably haven't been using in production for a long time now, but we're still bundling and do still shell out to in certain situations (I just couldn't remember whether any of them were ones we were doing in production). Now, we don't use bashbrew put-shared at all, and it can go away completely, and manifest-tool with it (which simplifies issues like #104).