Remove AcceleratorConnector.tpu_id

[DuYicong515]

What does this PR do?

Part of #11449: deprecate unused properties in accelerator_connector: tpu_id

AccleratorConnector.tpu_id was not used internally, and was not meant to be public. Remove it in favor of using Trainer.device_ids to check the TPU id when use TPU accelerator directly.

Does your PR introduce any breaking changes? If yes, please list them.

None

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Make sure you had fun coding 🙃

[krshrimali]

Thanks, @DuYicong515! Left a couple of comments, looking forward to your thoughts on them. :)

[kaushikb11]

Thanks for the clean up!

[tchaton]

Nice work !