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.

chuniio/chuniio.c

@@ -75,9 +75,6 @@ void chuni_io_jvs_poll(uint8_t *opbtn, uint8_t *beams)
     }
 }
 
-void chuni_io_jvs_set_coin_blocker(bool open)
-{}
-
 HRESULT chuni_io_slider_init(void)
 {
     return S_OK;