Revert "hydra: l0dables.nix args"

This reverts commit eccc8558.

hydra/l0dables.nix

-{ rustManifest ? ./channel-rust-nightly.toml,
-  mozillaOverlay ? import <mozillaOverlay>,
-  pkgs ? (import <nixpkgs> { overlays = [ mozillaOverlay ]; }),
-}:
 let
+  rustManifest = ./channel-rust-nightly.toml;
+  mozillaOverlay = import <mozillaOverlay>;
+  pkgs = (import <nixpkgs> { overlays = [ mozillaOverlay ]; });
   pkgs' = pkgs // {
     rustChannelOfTargets = _channel: _date: targets:
       (pkgs.lib.rustLib.fromManifestFile rustManifest {