[JAX] Remove code that sets or tests --jax_coordination_service.

--jax_coordination_service defaults to True and has for some time, and support for the non-coordination service case will be removed shortly.

PiperOrigin-RevId: 551932242

jax/experimental/multihost_utils.py

@@ -169,8 +169,7 @@ def reached_preemption_sync_point(step_id: int) -> bool:
   uses the next step id (i.e., max + 1) as the safe step to save a checkpoint.
   All hosts should continue training more steps until this method returns True,
   indicating that the `step_id` is equal to the safe step and the hosts should
-  start saving a checkpoint. This feature requires enabling
-  `jax.config.jax_coordination_service`.
+  start saving a checkpoint.
 
   To use this API, all hosts must start training from the same step and call at
   every training step. Example usage: