Remove some tpu_lib not used at all

PiperOrigin-RevId: 296140699

official/modeling/model_training_utils.py

@@ -24,7 +24,6 @@ import os
 from absl import logging
 import tensorflow as tf
 from official.utils.misc import distribution_utils
-from official.utils.misc import tpu_lib
 
 _SUMMARY_TXT = 'training_summary.txt'
 _MIN_SUMMARY_STEPS = 10

official/modeling/training/distributed_executor.py

@@ -31,7 +31,6 @@ import tensorflow as tf
 # pylint: disable=unused-import,g-import-not-at-top,redefined-outer-name,reimported
 from typing import Optional, Dict, List, Text, Callable, Union, Iterator, Any
 from official.modeling.hyperparams import params_dict
-from official.utils.misc import tpu_lib
 from official.utils.misc import distribution_utils
 from official.utils import hyperparams_flags