dh-buildinfo considered harmful

[kaduk]

CDBS pulled this in everywhere as part of @cdbs@ in control.in.
Now that we're not using control.in any more, as we convert packages to dh7, we need to remove dh-buildinfo (it is in build-depends ~everywhere but I don't think we are explicitly calling it in packages we've converted to dh7).
It is harmful because it installs a file in a global path that will differ for different architecture packages, causing multiarch to be useless; upstream seems to disrecommend it.