lib.makeScopeWithSplicing: provide default for keep,extra

These are often unneeded by the user.

pkgs/development/interpreters/python/passthrufun.nix

@@ -48,7 +48,6 @@
       };
       hooks = import ./hooks/default.nix;
       keep = lib.extends hooks pythonPackagesFun;
-      extra = _: {};
       optionalExtensions = cond: as: lib.optionals cond as;
       pythonExtension = import ../../../top-level/python-packages.nix;
       python2Extension = import ../../../top-level/python2-packages.nix;
@@ -61,7 +60,7 @@
       ]);
       aliases = self: super: lib.optionalAttrs config.allowAliases (import ../../../top-level/python-aliases.nix lib self super);
     in makeScopeWithSplicing {
-      inherit otherSplices keep extra;
+      inherit otherSplices keep;
       f = lib.extends (lib.composeExtensions aliases extensions) keep;
     }) {
       overrides = packageOverrides;