MB-10059 Remove the unnecessary check in getting a rev_seq value

Change-Id: I1757b5b0f8c2d58474faeabeb046e9363df3f346
Reviewed-on: http://review.couchbase.org/33502
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>