Remove unused errinfo field (will be removed from API)

Change-Id: Ib8cd1426d313ea9493076899f826250f07992a9a
Reviewed-on: http://review.couchbase.org/41639
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>