Drop support for lorri

Lorri does not cleanly integrate with my corporate device, which cannot run
NixOS. To expose dependencies to Emacs buffers, I will use nix-buffer.el, which
reads its values from dir-locals.nix. To easily expose dependencies from my
existing shell.nix files into dir-locals.nix, I wrote a Nix utility function.

.envrc

@@ -1 +1,6 @@
-eval "$(lorri direnv)"
+export BRIEFCASE="$(realpath ~/briefcase)"
+export DEPOT="$(realpath ~/depot)"
+export NIXPKGS="$(realpath ~/nixpkgs)"
+export NIX_PATH="nixpkgs=${NIXPKGS}:depot=${DEPOT}:briefcase=${BRIEFCASE}";
+export DESKTOP="zeno.lon.corp.google.com";
+export LAPTOP="seneca";