code: public OperationFuture<List<Server>> delete(ServerFilter filter) {
          List<Server> serverRefs = find(filter)
              .stream()
              .map(ServerMetadata::asRefById)
              .collect(toList());
  
          return delete(serverRefs.toArray(new Server[serverRefs.size()]));
      }
docs: Delete existing servers
  @param filter server filter object
  @return OperationFuture wrapper for list of ServerRef