Issue #23277: Remove more unused sys and os imports.

tests/test_clean.py

 """Tests for distutils.command.clean."""
-import sys
 import os
 import unittest
 import getpass

tests/test_config.py

 """Tests for distutils.pypirc.pypirc."""
-import sys
 import os
 import unittest
 import tempfile

tests/test_install_data.py

 """Tests for distutils.command.install_data."""
-import sys
 import os
 import unittest
 import getpass

tests/test_install_headers.py

 """Tests for distutils.command.install_headers."""
-import sys
 import os
 import unittest
 import getpass

tests/test_unixccompiler.py

 """Tests for distutils.unixccompiler."""
-import os
 import sys
 import unittest
 from test.support import EnvironmentVarGuard, run_unittest