CBQE-1124: remove indexed_key as required param

Change-Id: I8f8a9ad2611eeb9548e267504795b4c209f9efb9
Reviewed-on: http://review.couchbase.org/25091
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Thuan Nguyen <soccon@gmail.com>