Please describe the problem.

In recent nixpkgs the S3 special remotes have been disabled because some of the dependencies are quite old or unmaintained. More detail here: https://github.com/NixOS/nixpkgs/issues/45686

What steps will reproduce the problem?

Installing git-annex from the 18.09 nixpkgs release.

done; the esqueleto dep was dropped and deps are fairly current now. --Joey