platformio: fix eval

It used to fail with

error: do not use python3Packages when building Python packages, specify each used package as a separate argument

pkgs/development/embedded/platformio/default.nix

···
-{ newScope, python3Packages }:
+{ newScope }:
 
 let
   callPackage = newScope self;
 
   self = {
-    platformio-core = python3Packages.callPackage ./core.nix { };
+    platformio-core = callPackage ./core.nix { };
 
     platformio-chrootenv = callPackage ./chrootenv.nix { };
   };