removed DataFlushed arg of maybe_flush_docs_capi. it is always 0

Change-Id: I7ffc36639fc4f70ab409518fbb14508c171b81d6
Reviewed-on: http://review.couchbase.org/37556
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>