message: Remove cache_key_context None case
diff: @@ -3081,9 +3081,6 @@ class Function(object):
  assert not include_tensor_ranks_only
  hashable_input_signature = self._hashable_input_signature
  - if cache_key_context is None:
  - cache_key_context = self._cache_key_context()
  -
  (parent_graph, device_functions, colocation_stack, in_cross_replica_context,
  variable_policy, xla_context_id) = cache_key_context
  