bpo-29836: Remove nturl2path from test_sundry and amend the module docstring (GH-694)

The module is implicitly tested through test_urllib.

Lib/nturl2path.py

-"""Convert a NT pathname to a file URL and vice versa."""
+"""Convert a NT pathname to a file URL and vice versa.
+
+This module only exists to provide OS-specific code
+for urllib.requests, thus do not use directly.
+"""
+# Testing is done through test_urllib.
 
 def url2pathname(url):
     """OS-specific conversion from a relative URL of the 'file' scheme

Lib/test/test_sundry.py

@@ -6,8 +6,7 @@ import unittest
 
 class TestUntestedModules(unittest.TestCase):
     def test_untested_modules_can_be_imported(self):
-        untested = ('bdb', 'encodings', 'formatter',
-                    'nturl2path', 'tabnanny')
+        untested = ('bdb', 'encodings', 'formatter', 'tabnanny')
         with support.check_warnings(quiet=True):
             for name in untested:
                 try: