Remove duplicate code for getting all items from checkpoint

Change-Id: I320cddf9ecd7ae0947abaf33add5065ce50f442c
Reviewed-on: http://review.couchbase.org/41560
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>