Revert "MB-10794: Set the open checkpoint seqno properly when backfill ends"

This reverts commit a43f919e3a62c67af1a8f5fa1c4194ccae6252e7.

Change-Id: I96df3bd4e8cabcd0791bf69940e5be905cee8a32
Reviewed-on: http://review.couchbase.org/35563
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>