bpo-39682: make `pathlib.Path` immutable by removing (undocumented) support for "closing" a path by using it as a context manager (GH-18846)

Support for using a path as a context manager remains, and is now a no-op.
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 5b362a0..8b19cff 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -1720,13 +1720,15 @@
         next(it2)
         with p:
             pass
-        # I/O operation on closed path.
-        self.assertRaises(ValueError, next, it)
-        self.assertRaises(ValueError, next, it2)
-        self.assertRaises(ValueError, p.open)
-        self.assertRaises(ValueError, p.resolve)
-        self.assertRaises(ValueError, p.absolute)
-        self.assertRaises(ValueError, p.__enter__)
+        # Using a path as a context manager is a no-op, thus the following
+        # operations should still succeed after the context manage exits.
+        next(it)
+        next(it2)
+        p.exists()
+        p.resolve()
+        p.absolute()
+        with p:
+            pass
 
     def test_chmod(self):
         p = self.cls(BASE) / 'fileA'