refactor(snix/shell): drop josh functionality

Snix is not provided as a josh workspace, this was only the case for
Tvix, while still in the TVL repo, so we can drop that entrypoint.

Change-Id: Iafc2a6520645e607f26bcf674a3d98b646f5c9f2
Reviewed-on: https://cl.snix.dev/c/snix/+/30601
Reviewed-by: Yureka <snix@yuka.dev>
Tested-by: besadii
Autosubmit: Florian Klink <flokli@flokli.de>

snix/shell.nix

@@ -1,17 +1,4 @@
-# This file is shell.nix in the snix josh workspace,
-# *and* used to provide the //snix:shell attribute in a full depot checkout.
-# Hence, it may not use depot as a toplevel argument.
-
-{
-  # This falls back to the snix josh workspace-provided nixpkgs checkout.
-  # In the case of depot, it's always set explicitly.
-  pkgs ? (import ./nixpkgs {
-    depotOverlays = false;
-    depot.third_party.sources = import ./sources { };
-  })
-, withIntegration ? false
-, ...
-}:
+{ pkgs, ... }:
 
 pkgs.mkShell {
   name = "snix-rust-dev-env";
@@ -40,7 +27,6 @@ pkgs.mkShell {
     pkgs.protobuf
   ] ++ pkgs.lib.optionals pkgs.stdenv.isLinux [
     pkgs.runc
-  ] ++ pkgs.lib.optionals withIntegration [
     pkgs.cbtemulator
     pkgs.google-cloud-bigtable-tool
   ];