After #16017 there were a lot
of comments saying that `nix` would be better than `JSON`
for Go packages dependency sets.
As said in https://github.com/NixOS/nixpkgs/pull/16017#issuecomment-229624046
> Because of the content-addressable store, if two programs have the
> same dependency it will already result in the same derivation in
> the
> store. Git also has compression in the pack files so it won't make
> much difference to duplicate the dependencies on disk. And finally
> most users will just use the binary builds so it won't make any
> differences to them.
This PR removes `libs.json` file and puts all package dependencies in
theirs `deps.json`.
