Don't save target_policy as a class member since it is only used once, to create self._target_greedy_policy.
Don't save target_policy as a class member since it is only used once, to create self._target_greedy_policy.

PiperOrigin-RevId: 264246858
Change-Id: I267be016d9751dfe55a9631a08dd5f6da3769ec9

tensorflow/agents,tensorflow/agents