Issue #23209: Revert change on selectors, test_selectors failed.
diff --git a/Lib/selectors.py b/Lib/selectors.py
index b2f4c2b..e4ad4cb 100644
--- a/Lib/selectors.py
+++ b/Lib/selectors.py
@@ -256,7 +256,6 @@
 
     def close(self):
         self._fd_to_key.clear()
-        self._map = None
 
     def get_map(self):
         return self._map