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.

chunihook/chuni-dll.h

@@ -9,7 +9,6 @@ struct chuni_dll {
     HRESULT (*jvs_init)(void);
     void (*jvs_poll)(uint8_t *opbtn, uint8_t *beams);
     void (*jvs_read_coin_counter)(uint16_t *total);
-    void (*jvs_set_coin_blocker)(bool open);
     HRESULT (*slider_init)(void);
     void (*slider_start)(chuni_io_slider_callback_t callback);
     void (*slider_stop)(void);