Check whether register_keras_serializable is actually necessary

trieste/models/keras/utils.py

@@ -14,23 +14,14 @@
 
 from __future__ import annotations
 
-from typing import Callable, Optional
+from typing import Optional
 
 import tensorflow as tf
 import tensorflow_probability as tfp
-from gpflow.keras import tf_keras
 
 from ...data import Dataset
 from ...types import TensorType
 
-try:
-    register_keras_serializable = tf_keras.saving.register_keras_serializable()
-except AttributeError:  # pragma: no cover (tested but not by coverage)
-
-    # not required in earlier version of TF
-    def register_keras_serializable(func: Callable[..., object]) -> Callable[..., object]:
-        return func
-
 
 def get_tensor_spec_from_data(dataset: Dataset) -> tuple[tf.TensorSpec, tf.TensorSpec]:
     r"""
@@ -131,7 +122,6 @@ def sample_model_index(
     return indices
 
 
-@register_keras_serializable
 def negative_log_likelihood(
     y_true: TensorType, y_pred: tfp.distributions.Distribution
 ) -> TensorType: