Avoid “error: None” messages from distutils (#4931).

Thanks to Amaury Forgeot d’Arc and Philip J. Eby.

Lib/distutils/dir_util.py

@@ -2,7 +2,7 @@
 
 Utility functions for manipulating directories and directory trees."""
 
-import os, sys
+import os
 import errno
 from distutils.errors import DistutilsFileError, DistutilsInternalError
 from distutils import log
@@ -182,7 +182,6 @@ def remove_tree(directory, verbose=1, dry_run=0):
     Any errors are ignored (apart from being reported to stdout if 'verbose'
     is true).
     """
-    from distutils.util import grok_environment_error
     global _path_created
 
     if verbose >= 1:
@@ -199,8 +198,7 @@ def remove_tree(directory, verbose=1, dry_run=0):
             if abspath in _path_created:
                 del _path_created[abspath]
         except (IOError, OSError) as exc:
-            log.warn(grok_environment_error(
-                    exc, "error removing %s: " % directory))
+            log.warn("error removing %s: %s", directory, exc)
 
 def ensure_relative(path):
     """Take the full path 'path', and make it a relative path.