Remove private Keras imports.

PiperOrigin-RevId: 563439874

Author: fchollet

tensorflow_model_optimization/python/core/quantization/keras/default_8bit/default_8bit_transforms.py

@@ -29,10 +29,17 @@
 from tensorflow_model_optimization.python.core.quantization.keras.graph_transformations import transforms
 
 try:
-  from keras.backend import unique_object_name  # pylint: disable=g-import-not-at-top
+  # OSS
+  import keras  # pylint: disable=g-import-not-at-top
+  if hasattr(keras, 'src'):
+    # Path as seen in pip packages as of TF/Keras 2.13.
+    from keras.src.backend import unique_object_name  # pylint: disable=g-import-not-at-top
+  else:
+    from keras.backend import unique_object_name  # pylint: disable=g-import-not-at-top,g-importing-member
 except ImportError:
-  # Path as seen in pip packages as of TF/Keras 2.13.
-  from keras.src.backend import unique_object_name  # pylint: disable=g-import-not-at-top
+  # Internal
+  unique_object_name = tf._keras_internal.backend.unique_object_name  # pylint: disable=protected-access
+
 
 LayerNode = transforms.LayerNode
 LayerPattern = transforms.LayerPattern