Makes some helper functions in `bandits.agents.examples.v2.trainer.py` private
Makes some helper functions in `bandits.agents.examples.v2.trainer.py` private

They are not to be used outside of this module.

PiperOrigin-RevId: 483413990
Change-Id: I10c5765e4d7f9daf4ef215565afed44c1e394d96

tensorflow/agents,tensorflow/agents