feat(tvix/eval): move shell.nix and .envrc to //tvix

Both //tvix/eval and //tvix/nix_cli have need to for rust tooling available
in $PATH.

Move this one level up, so it's accessible in all subdirectories.

Change-Id: I0763bbe9cefdc962f3a8f86c51e8f67cde8b4b04
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7248
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

tvix/eval/.envrc

@@ -1,7 +0,0 @@
-if command -v lorri >/dev/null; then
-  eval "$(lorri direnv)"
-else
-  use nix
-fi
-
-source_up

tvix/eval/shell.nix

@@ -1,14 +0,0 @@
-{ depot ? import ../../. { }
-, pkgs ? depot.third_party.nixpkgs
-}:
-
-pkgs.mkShell {
-  name = "tvix-eval-dev-env";
-  packages = [
-    pkgs.cargo
-    pkgs.clippy
-    pkgs.rust-analyzer
-    pkgs.rustc
-    pkgs.rustfmt
-  ];
-}