Clean up compatibility code in importlib fixtures (GH-19156) (#19543)

(cherry picked from commit 574547a)

Co-authored-by: Jason R. Coombs <[email protected]>

Co-authored-by: Jason R. Coombs <[email protected]>

Author: miss-islington

Lib/test/test_importlib/fixtures.py

@@ -1,25 +1,11 @@
-from __future__ import unicode_literals
-
 import os
 import sys
 import shutil
+import pathlib
 import tempfile
 import textwrap
 import contextlib
 
-try:
-    from contextlib import ExitStack
-except ImportError:
-    from contextlib2 import ExitStack
-
-try:
-    import pathlib
-except ImportError:
-    import pathlib2 as pathlib
-
-
-__metaclass__ = type
-
 
 @contextlib.contextmanager
 def tempdir():
@@ -58,7 +44,7 @@ def install_finder(finder):
 
 class Fixtures:
     def setUp(self):
-        self.fixtures = ExitStack()
+        self.fixtures = contextlib.ExitStack()
         self.addCleanup(self.fixtures.close)