Remove barrier test in pjrt/distributed with equivalent test coverage…

… in coordination service's fork of client_server_test.

1. This is in preparation for a change in barrier semantics (don't require users to specify unique ids).

2. Moving forward, we want to shift new business logic tests to be in coord service's test suite.

This allows us to cover more edge cases with intrusive hooks (e.g. agent dtor tests) as well as non-Jax (i.e. TF) scenarios.

3. Only use pjrt/distributed tests + Jax multi-process Python tests for Jax-specific requirements (e.g. topology exchange contract), or to exercise the xla_client (nanobind) and pjrt/distributed codepaths to validate that args are plumbed correctly.

This reduces review burden on the Jax team.

PiperOrigin-RevId: 693752761

xla/pjrt/distributed/client_server_test.cc

@@ -899,37 +899,6 @@ TEST_F(ClientServerTest, WaitAtBarrier_TimeoutWithDifferentBarrierId) {
   }
 }
 
-TEST_F(ClientServerTest, WaitAtBarrier_FailWithSameBarrierId) {
-  int num_nodes = 2;
-  StartService(num_nodes);
-
-  auto thread_fn = [&](int node_id) -> absl::Status {
-    auto client = GetClient(node_id);
-    TF_RETURN_IF_ERROR(client->Connect());
-
-    TF_RETURN_IF_ERROR(
-        client->WaitAtBarrier("barrier_1", kBarrierTimeout, std::nullopt));
-    TF_RETURN_IF_ERROR(
-        client->WaitAtBarrier("barrier_1", kBarrierTimeout, std::nullopt));
-
-    TF_RETURN_IF_ERROR(client->Shutdown());
-    return absl::OkStatus();
-  };
-
-  std::vector<absl::Status> statuses(num_nodes);
-  {
-    tsl::thread::ThreadPool thread_pool(tsl::Env::Default(), "test_threads",
-                                        num_nodes);
-    for (int i = 0; i < num_nodes; ++i) {
-      thread_pool.Schedule([&, i]() { statuses[i] = thread_fn(i); });
-    }
-  }
-  for (int i = 0; i < num_nodes; ++i) {
-    EXPECT_EQ(statuses[i].code(), tsl::error::FAILED_PRECONDITION)
-        << " node id: " << i;
-  }
-}
-
 TEST_F(ClientServerTest, WaitAtBarrierSubset_Succeeds) {
   int num_nodes = 3;
   StartService(num_nodes);