Remove imports of 'warnings' that are no longer needed in dummy_thread,
filecmp, and shelve.
diff --git a/Misc/NEWS b/Misc/NEWS
index 4a92186..99414d1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -48,6 +48,8 @@
 Library
 -------
 
+- Remove unneeded imports of 'warnings' from shelve, filecmp, and dummy_thread.
+
 - Issue #3575: Incremental decoder's decode function now takes bytearray
   by using 's*' instead of 't#'.