Remove unused snapshotVBState flag variable.

Change-Id: I1f8e471dc91ac8b3a6f027b518d587567e7a650a
Reviewed-on: http://review.couchbase.org/39905
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>