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.

monzo_ynab/.envrc

@@ -1,14 +1,7 @@
-# source_up traversing up directories until it finds the nearest .envrc file,
-# which it uses to extend the environment in this .envrc.
-#
-# Since ../.envrc calls `eval "$(lorri direnv)"`, the buildInputs and variables
-# definitions inside of the attribute set passed to pkgs.mkShell become
-# available here as well.
 source_up
 export monzo_client_id="$(pass show finance/monzo/client-id)"
 export monzo_client_secret="$(pass show finance/monzo/client-secret)"
-export store_path="$(pwd)"
 export ynab_personal_access_token="$(pass show finance/youneedabudget.com/personal-access-token)"
 export ynab_account_id="$(pass show finance/youneedabudget.com/personal-access-token)"
 export ynab_budget_id="$(pass show finance/youneedabudget.com/budget-id)"
-eval "$(lorri direnv)"
+export store_path="$(pwd)"

monzo_ynab/dir-locals.nix

@@ -0,0 +1,3 @@
+let
+  briefcase = import <briefcase> {};
+in briefcase.utils.nixBufferFromShell ./shell.nix

monzo_ynab/shell.nix

@@ -1,11 +1,9 @@
-{ pkgs, briefcase, ... }:
-
-pkgs.mkShell {
+let
+  pkgs = import <nixpkgs> {};
+in pkgs.mkShell {
   buildInputs = [
     pkgs.go
     pkgs.goimports
     pkgs.godef
-    briefcase.monzo_ynab.job
-    briefcase.monzo_ynab.tokens
   ];
 }