core (memory): fixed a double timer.cancel in Sessions

src/memory/memory.py

@@ -123,9 +123,7 @@ class Sessions(object):
         raise NotImplementedError("You need do use newSession to create a session")
 
     def __delitem__(self, session_id):
-        """ Cancel the timer, then actually delete the session data """
-        timer = self._sessions[session_id][0]
-        timer.cancel()
+        """ delete the session data """
         self._purgeSession(session_id)
 
     def keys(self):