Remove the deprecated Python rabit module. (#9523)

tests/python/test_collective.py

@@ -39,37 +39,6 @@ def test_rabit_communicator():
         assert worker.exitcode == 0
 
 
-# TODO(rongou): remove this once we remove the rabit api.
-def run_rabit_api_worker(rabit_env, world_size):
-    with xgb.rabit.RabitContext(rabit_env):
-        assert xgb.rabit.get_world_size() == world_size
-        assert xgb.rabit.is_distributed()
-        assert xgb.rabit.get_processor_name().decode() == socket.gethostname()
-        ret = xgb.rabit.broadcast('test1234', 0)
-        assert str(ret) == 'test1234'
-        ret = xgb.rabit.allreduce(np.asarray([1, 2, 3]), xgb.rabit.Op.SUM)
-        assert np.array_equal(ret, np.asarray([2, 4, 6]))
-
-
-# TODO(rongou): remove this once we remove the rabit api.
-def test_rabit_api():
-    world_size = 2
-    tracker = RabitTracker(host_ip='127.0.0.1', n_workers=world_size)
-    tracker.start(world_size)
-    rabit_env = []
-    for k, v in tracker.worker_envs().items():
-        rabit_env.append(f"{k}={v}".encode())
-    workers = []
-    for _ in range(world_size):
-        worker = multiprocessing.Process(target=run_rabit_api_worker,
-                                         args=(rabit_env, world_size))
-        workers.append(worker)
-        worker.start()
-    for worker in workers:
-        worker.join()
-        assert worker.exitcode == 0
-
-
 def run_federated_worker(port, world_size, rank):
     with xgb.collective.CommunicatorContext(xgboost_communicator='federated',
                                             federated_server_address=f'localhost:{port}',