Update imports from Keras applications

PiperOrigin-RevId: 486136890

research/object_detection/models/keras_models/resnet_v1.py

@@ -18,17 +18,13 @@
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
+from keras.applications import resnet
 
 import tensorflow.compat.v1 as tf
 
 from object_detection.core import freezable_batch_norm
 from object_detection.models.keras_models import model_utils
 
-try:
-  from keras.applications import resnet  # pylint:disable=g-import-not-at-top
-except ImportError:
-  from tensorflow.python.keras.applications import resnet  # pylint:disable=g-import-not-at-top
-
 
 def _fixed_padding(inputs, kernel_size, rate=1):  # pylint: disable=invalid-name
   """Pads the input along the spatial dimensions independently of input size.

research/object_detection/models/ssd_efficientnet_bifpn_feature_extractor.py

@@ -19,16 +19,17 @@ from __future__ import division
 from __future__ import print_function
 
 from absl import logging
+from keras import backend as keras_backend
 from six.moves import range
 from six.moves import zip
 import tensorflow.compat.v2 as tf
 
-from tensorflow.python.keras import backend as keras_backend
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import bidirectional_feature_pyramid_generators as bifpn_generators
 from object_detection.utils import ops
 from object_detection.utils import shape_utils
 from object_detection.utils import tf_version
+
 # pylint: disable=g-import-not-at-top
 if tf_version.is_tf2():
   try: