mcreq: Remove unused 'remaining' field

Change-Id: I7da3c3184b7f6e57cbe8dba08ebdf3046660dd02
Reviewed-on: http://review.couchbase.org/39882
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>