Remove unused comments related to Python 2 compatibility.

PiperOrigin-RevId: 437767104

research/object_detection/export_tflite_graph_lib_tf2.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/export_tflite_graph_lib_tf2_test.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/export_tflite_graph_tf2.py

-# Lint as: python2, python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/export_tflite_ssd_graph.py

-# Lint as: python2, python3
 # Copyright 2018 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/export_tflite_ssd_graph_lib.py

-# Lint as: python2, python3
 # Copyright 2018 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/export_tflite_ssd_graph_lib_tf1_test.py

-# Lint as: python2, python3
 # Copyright 2018 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/exporter_lib_tf2_test.py

-# Lint as: python2, python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/exporter_lib_v2.py

-# Lint as: python2, python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/exporter_main_v2.py

-# Lint as: python2, python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/exporter_tf1_test.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/context_rcnn_lib.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/context_rcnn_lib_tf1_test.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/context_rcnn_lib_tf2.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/context_rcnn_lib_tf2_test.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/faster_rcnn_meta_arch_test.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/meta_architectures/ssd_meta_arch_test.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/model_main_tf2.py

-# Lint as: python3
 # Copyright 2020 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/models/embedded_ssd_mobilenet_v1_feature_extractor.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/models/faster_rcnn_nas_feature_extractor.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

research/object_detection/models/faster_rcnn_pnas_feature_extractor.py

-# Lint as: python2, python3
 # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");