Enable v2 layers for resnet_model.

PiperOrigin-RevId: 287370879

Author: alanchiao

official/vision/image_classification/resnet_model.py

@@ -27,16 +27,13 @@
 from __future__ import division
 from __future__ import print_function
 
-import tensorflow as tf
-
 from tensorflow.python.keras import backend
 from tensorflow.python.keras import initializers
+from tensorflow.python.keras import layers
 from tensorflow.python.keras import models
 from tensorflow.python.keras import regularizers
 from official.vision.image_classification import imagenet_preprocessing
 
-layers = tf.keras.layers
-
 L2_WEIGHT_DECAY = 1e-4
 BATCH_NORM_DECAY = 0.9
 BATCH_NORM_EPSILON = 1e-5