Drop code for testing for Windows in build script

build.py

@@ -32,7 +32,6 @@
 import shutil
 import stat
 import subprocess
-import sys
 import tarfile
 import tempfile
 import textwrap
@@ -119,11 +118,6 @@ def download_source(self, directory: pathlib.Path) -> None:
 ]
 
 
-# def _is_windows() -> bool:
-#     """Return True if the current platform is Windows."""
-#     return sys.platform == "win32"
-
-
 def _assert_detect_command(cmd: list[str]) -> None:
     """
     Run the given command in a subprocess and write its outputs to stdout.