message: Simplify Huber Loss implementation
diff: @@ -1538,7 +1538,7 @@ def huber(y_true, y_pred, delta=1.0):
  ```
  loss = 0.5 * x^2 if |x| <= d
  - loss = 0.5 * d^2 + d * (|x| - d) if |x| > d
  + loss = d * |x| - 0.5 * d^2 if |x| > d
  ```
  where d is `delta`. See: https://en.wikipedia.org/wiki/Huber_loss
  @@ -1559,8 +1559,8 @@ def huber(y_true, y_pred, delta=1.0):
  half = ops.convert_to_tensor_v2_with_dispatch(0.5, dtype=abs_error.dtype)
  return K.mean(
  array_ops.where_v2(
  - abs_error <= delta, half * math_ops.pow(error, 2),
  - half * math_ops.pow(delta, 2) + delta * (abs_error - delta)),
  + abs_error <= delta, half * math_ops.square(error),
  + delta * abs_error - half * math_ops.square(delta)),
  axis=-1)
  