Remove obj.valid from documentation

Fixes: #341


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3241 d4fa192b-c00b-0410-8231-f00ffab90ce4

man/vcl.7so

@@ -511,8 +511,6 @@ The HTTP protocol version used when the object was retrieved.
 The HTTP status code returned by the server.
 .It Va obj.response
 The HTTP status message returned by the server.
-.It Va obj.valid
-True if the request resulted in a valid HTTP response.
 .It Va obj.cacheable
 True if the request resulted in a cacheable response.
 .\" see cache_center.c and rfc2616.c for details