Drop support for dir-locals.nix, <nixpkgs>, etc.

In the spirit of Marie Kondo, I'm tidying up!

TL;DR:
- Prefer .envrc `use_nix` and delete all dir-locals.nix files
- Remove ~all references to <nixpkgs>, <unstable>, <depot> and prefer
  referencing each with briefcase.third_party.{pkgs,unstable,depot}
- Delete nixBufferFromShell function since I was only using that in
  dir-locals.nix files

1 files changed, 6 insertions, 5 deletions

diff --git a/boilerplate/elm/shell.nix b/boilerplate/elm/shell.nix
index 6f1c8ee23b30..00bb4b0b3edc 100644
--- a/boilerplate/elm/shell.nix
+++ b/boilerplate/elm/shell.nix
@@ -1,9 +1,10 @@
 let
-  pkgs = import <nixpkgs> {};
+  briefcase = import <briefcase> {};
+  pkgs = briefcase.third_party.pkgs;
 in pkgs.mkShell {
-  buildInputs = with pkgs; [
-    elmPackages.elm
-    elmPackages.elm-format
-    elmPackages.elm-live
+  buildInputs = with pkgs.elmPackages; [
+    elm
+    elm-format
+    elm-live
   ];
 }