Removed (unused) support for disabling cas

Change-Id: I983ad76a5b93c78b486c5a842438ae7cdc65c839
Reviewed-on: http://review.couchbase.org/33076
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>