test io_flush/many_data: disable on reference count mode
test io_flush/many_data: disable on reference count mode

Because this is very slow.

kenhys/groonga,kenhys/groonga,komainu8/groonga,groonga/groonga,groonga/groonga,kenhys/groonga,komainu8/groonga,groonga/groonga,groonga/groonga,naoa/groonga,naoa/groonga,naoa/groonga,komainu8/groonga,groonga/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,komainu8/groonga,naoa/groonga,groonga/groonga,kenhys/groonga,naoa/groonga,komainu8/groonga,komainu8/groonga,komainu8/groonga,komainu8/groonga,naoa/groonga,naoa/groonga