[Misc] Clean up useless code (#19889)

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

vllm/config.py

@@ -1900,17 +1900,6 @@ class ParallelConfig:
             os.environ["VLLM_ENABLE_V1_MULTIPROCESSING"] = "0"
             logger.info("Disabling V1 multiprocessing for external launcher.")
 
-        ray_only_devices: list[str] = []
-        from vllm.platforms import current_platform
-        if (current_platform.device_type in ray_only_devices
-                and self.world_size > 1):
-            if self.distributed_executor_backend is None:
-                self.distributed_executor_backend = "ray"
-            if self.distributed_executor_backend != "ray":
-                raise ValueError(
-                    f"{current_platform.device_type.upper()} backend only "
-                    "supports Ray for distributed inference.")
-
         if self.distributed_executor_backend is None and self.world_size > 1:
             # We use multiprocessing by default if world_size fits on the
             # current node and we aren't in a ray placement group.