gh-89520: IDLE - Fix test_exists_user cleanup to properly remove section

read_dict is additive and doesn't remove sections. Setting enable to
False still leaves the ZzDummy section in user config. Use
remove_section to fully restore the original empty state.

Author: gpshead

Lib/idlelib/idle_test/test_zzdummy.py

@@ -99,9 +99,7 @@ def test_exists_user(self):
         self.assertEqual(zzdummy.idleConf.GetExtensionKeys("ZzDummy"), {'<<z-in>>': ['<Control-Shift-KeyRelease-Insert>']})
         self.assertEqual(zzdummy.idleConf.GetExtensionBindings("ZzDummy"), {'<<z-in>>': ['<Control-Shift-KeyRelease-Insert>'], '<<z-out>>': ['<Control-Shift-KeyRelease-Delete>']})
         # Restore
-        zzdummy.idleConf.userCfg["extensions"].read_dict({
-            "ZzDummy": {'enable': 'False'}
-        })
+        zzdummy.idleConf.userCfg["extensions"].remove_section("ZzDummy")
 
     def test_init(self):
         zz = self.zz