PSv2: Remove a TODO that has been addressed.

PiperOrigin-RevId: 328129947
Change-Id: If3fc9bd3ccb4a271c60e48e052969c07174326e4

tensorflow/python/distribute/client/client.py

@@ -985,8 +985,6 @@ class Client(object):
         scheduled function since the last time an error was thrown or since
         the beginning of the program.
     """
-    # TODO(b/159486639): Update the docs once we can cancel the functions being
-    # executed on workers, that when `join` returns, the system is stabilized.
     with _translate_parameter_server_failure():
       self.cluster.join()