MB-100 get rid of redundant rewrite_key_value_tuples function

Change-Id: I802b10f1c2331580f1c9a7300a36ba2c13343486
Reviewed-on: http://review.couchbase.org/28322
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>