Merge pull request #12557 from grpc/updatedoc

Update service_config doc

doc/service_config.md

@@ -24,10 +24,7 @@ The service config is a JSON string of the following form:
   // opposed to backend addresses), gRPC will use grpclb (see
   // https://github.com/grpc/grpc/blob/master/doc/load-balancing.md),
   // regardless of what LB policy is requested either here or via the
-  // client API.  However, if the resolver returns at least one backend
-  // address in addition to the balancer address(es), the client may fall
-  // back to the requested policy if it is unable to reach any of the
-  // grpclb load balancers.
+  // client API.
   'loadBalancingPolicy': string,
 
   // Per-method configuration.  Optional.