Don't convert the expiration time in SetWithMeta / DelWithMeta.

As SetWithMeta and DelWithMeta request packets contain the
absolute expiration time, we should not convert them to the
absolute time again.

Change-Id: If8737d30eb75a64087edea7ddf04aa99e568ad8f
Reviewed-on: http://review.couchbase.org/37077
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>