The main output started to retain dependency on bootstrap-tools; see
https://github.com/NixOS/nixpkgs/pull/15867#issuecomment-227949096
This reverts commit c05d8295988697adbb920a7b4a999ae3670c5504, reversing
changes made to f073df60d60444c30c49cb26d6b187a4100b41fe.
Looks like `nix-env -qaP --drv-path` is not enough and one need to
either add `--json` too to catch problems like this... or just use
`nox-review wip`.
