Remove unncessary API function export

This function is not meant to be available outside
the couchstore library.

Change-Id: If8fc5f82b133e879c15bafe97749be8ad11af8de
Reviewed-on: http://review.couchbase.org/27313
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>