Is there any iRule command in HTTP event to remove HTTP response code?

Yes, iRules do allow you to change the HTTP

versions for both the request and responses. With that said, re-writing the versions should be done with caution because the client may not support the version you are changing to. In any case here is the rule.

    
    when HTTP_RESPONSE {    
      HTTP::version "0.9"    
      HTTP::close    
    }