Revert "cpython: fix finding headers when cross-compiling extension modules"

This breaks virtualenv https://github.com/NixOS/nixpkgs/issues/104483.
We should probably not move `_sysconfigdata` but just copy it for cross to
another place or output.

This reverts commit 11806b6ede.

pkgs/development/python-modules/bootstrapped-pip/default.nix

@@ -45,7 +45,7 @@ stdenv.mkDerivation rec {
     mv wheel* wheel
     # Set up PYTHONPATH. The above folders need to be on PYTHONPATH
     # $out is where we are installing to and takes precedence
-    export PYTHONPATH="$out/${python.sitePackages}:$(pwd)/pip/src:$(pwd)/setuptools:$(pwd)/setuptools/pkg_resources:$(pwd)/wheel:$PYTHONPATH"
+    export PYTHONPATH="$out/${python.sitePackages}:$(pwd)/pip/src:$(pwd)/setuptools:$(pwd)/setuptools/pkg_resources:$(pwd)/wheel"
 
     echo "Building setuptools wheel..."
     pushd setuptools