MB-12063: Properly save the max deleted seqno during vb snapshots

Change-Id: Ife9e3b26956638622de0427cd573cd4d37c7e443
Reviewed-on: http://review.couchbase.org/40997
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>