Fix dense depth loss and model, fix metric naming

metric.py

@@ -1,7 +1,7 @@
 import tensorflow as tf
 
 
-def delta1_metric(y_true, y_pred):
+def delta1(y_true, y_pred):
     max_ratio = tf.maximum(y_pred / y_true, y_true / y_pred)
     return tf.reduce_mean(tf.cast(max_ratio < tf.convert_to_tensor(1.25), tf.float32))