clean 'WG_BACKEND' unused code. (#258)

verl/single_controller/base/worker.py

@@ -42,10 +42,8 @@ class WorkerHelper:
             if os.getenv("WG_BACKEND", None) == "ray":
                 import ray
                 return ray._private.services.get_node_ip_address()
-            elif os.getenv("WG_BACKEND", None) == "torch_rpc":
-                from verl.single_controller.torchrpc.k8s_client import get_ip_addr
-                return get_ip_addr()
-            return None
+            else:
+                raise NotImplementedError("WG_BACKEND now just support ray mode.")
 
         host_ipv4 = os.getenv("MY_HOST_IP", None)
         host_ipv6 = os.getenv("MY_HOST_IPV6", None)