Do some cleanup in importlib:

+ Ditch using arguments to super().
+ Ditch subclassing from object directly.
+ Move directory check out of chaining path hook to file path hook/finder.
+ Rename some classes to better reflect they are finders, not importers.

Lib/importlib/test/extension/test_path_hook.py

@@ -14,7 +14,7 @@ class PathHookTests(unittest.TestCase):
     # XXX Should it only work for directories containing an extension module?
 
     def hook(self, entry):
-        return importlib.ExtensionFileImporter(entry)
+        return importlib.ExtensionFileFinder(entry)
 
     def test_success(self):
         # Path hook should handle a directory where a known extension module