Delete coin blocker exports from IO DLLs

These never get called at the moment, so we have no way of
guaranteeing that any existing implementations are even correct. If
we do decide to start emulating the coin blocker then we will need
to advance the API versions, which will (hopefully) force any
third-party devs to test their coin blocker code before opting in.

divaio/divaio.c

@@ -72,9 +72,6 @@ void diva_io_jvs_read_coin_counter(uint16_t *out)
     *out = diva_io_coins;
 }
 
-void diva_io_jvs_set_coin_blocker(bool open)
-{}
-
 HRESULT diva_io_slider_init(void)
 {
     return S_OK;