Since Esqueleto is seemingly abandoned and it's causing grief with NixOS: https://git-annex.branchable.com/bugs/Old_dependencies_are_causing_pain_with_NixOS_18.09/ I did the work to remove it as a dependency in this commit https://github.com/seanparsons/git-annex/commit/62f291262f37327d9b2a864cd701aacb03766115

Alongside that is a bunch of nix specific files that support the building and/or development of git-annex, which is pretty much anything with "nix" in the name in the patch.