Remove duplicate code for getting number of items for a cursor

We no longer need this function because the getNumItemsForCursor()
function can be used to figure out how many items are remaining
for the persistence cursor.

Change-Id: Ibe5a515785dbaa2c3d40582d855504079b3a83f2
Reviewed-on: http://review.couchbase.org/41507
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>