bpo-35770: IDLE macosx deletes Options => Configure IDLE. (GH-11614)

It previously deleted Window => Zoom Height by mistake.
(Zoom Height is now on the Options menu).  On Mac, the settings
dialog is accessed via Preferences on the IDLE menu.
diff --git a/Lib/idlelib/macosx.py b/Lib/idlelib/macosx.py
index 9be4ed2..d6a1b37 100644
--- a/Lib/idlelib/macosx.py
+++ b/Lib/idlelib/macosx.py
@@ -178,7 +178,7 @@
     del mainmenu.menudefs[-1][1][0:2]
     # Remove the 'Configure Idle' entry from the options menu, it is in the
     # application menu as 'Preferences'
-    del mainmenu.menudefs[-2][1][0]
+    del mainmenu.menudefs[-3][1][0:1]
     menubar = Menu(root)
     root.configure(menu=menubar)
     menudict = {}