Merge pull request #9040 from minrk/rm-extension-del

remove unregister trait-change callback in ExtensionManager.__del__

IPython/core/extensions.py

@@ -59,11 +59,6 @@ def __init__(self, shell=None, **kwargs):
         )
         self.loaded = set()
 
-    def __del__(self):
-        self.shell.on_trait_change(
-            self._on_ipython_dir_changed, 'ipython_dir', remove=True
-        )
-
     @property
     def ipython_extension_dir(self):
         return os.path.join(self.shell.ipython_dir, u'extensions')