[3.9] bpo-41841: revise header (GH-24634)

Author: terryjreedy

Lib/idlelib/NEWS.txt

@@ -1,6 +1,6 @@
-What's New in IDLE 3.9.2
-Released on 2021-02-15?
-======================================
+What's New in IDLE 3.9.z
+(since 3.9.0)
+=========================
 
 
 bpo-43283: Document why printing to IDLE's Shell is often slower than
@@ -18,11 +18,6 @@ bpo-33065: Fix problem debugging user classes with __repr__ method.
 bpo-32631: Finish zzdummy example extension module: make menu entries
 work; add docstrings and tests with 100% coverage.
 
-
-What's New in IDLE 3.9.1
-Released on 2020-12-07
-======================================
-
 bpo-42508: Keep IDLE running on macOS.  Remove obsolete workaround
 that prevented running files with shortcuts when using new universal2
 installers built on macOS 11.