steam: actually propagate flags to the runtime, now from chrootenv wrapper

Example: instead of

(steamPackages.override { newStdcpp = true; }).steam-chrootenv

(which wasn't working anyway) you now do just:

steam.override { newStdcpp = true; }

pkgs/games/steam/default.nix

@@ -1,17 +1,11 @@
-{ pkgs, newScope
-, nativeOnly ? false
-, runtimeOnly ? false
-, newStdcpp ? false
-}:
+{ pkgs, newScope }:
 
 let
   callPackage = newScope self;
 
   self = rec {
     steam-runtime = callPackage ./runtime.nix { };
-    steam-runtime-wrapped = callPackage ./runtime-wrapped.nix {
-      inherit nativeOnly runtimeOnly newStdcpp;
-    };
+    steam-runtime-wrapped = callPackage ./runtime-wrapped.nix { };
     steam = callPackage ./steam.nix { };
     steam-chrootenv = callPackage ./chrootenv.nix { };
     steam-fonts = callPackage ./fonts.nix { };