Remove the legacy functions
  
    isdn_slot_readbchan(int slot, u_char *, u_char *, int);
    isdn_slot_driver(int slot);
    isdn_slot_channel(int slot);
    isdn_slot_set_usage(int slot, int usage);
    isdn_drv_writebuf_skb(int di, int ch, int x, struct sk_buff *skb);
    isdn_drv_hdrlen(int di);
  
Most of their tasks have been taken over by isdn_common.c, or are
obsoleted by using the isdn_slot based approach.