I can confirm that the following structs have not been used since at least OpenBSD 4.9. From Edgar Pettijohn.
Ok? Index: dhcpd.h =================================================================== RCS file: /cvs/src/usr.sbin/dhcpd/dhcpd.h,v retrieving revision 1.65 diff -u -p -r1.65 dhcpd.h --- dhcpd.h 31 Jul 2017 19:00:40 -0000 1.65 +++ dhcpd.h 1 Aug 2017 22:41:34 -0000 @@ -73,25 +73,6 @@ struct option_data { u_int8_t *data; }; -struct string_list { - struct string_list *next; - char *string; -}; - -/* A name server, from /etc/resolv.conf. */ -struct name_server { - struct name_server *next; - struct sockaddr_in addr; - time_t rcdate; -}; - -/* A domain search list element. */ -struct domain_search_list { - struct domain_search_list *next; - char *domain; - time_t rcdate; -}; - /* A dhcp packet and the pointers to its option values. */ struct packet { struct dhcp_packet *raw; @@ -294,12 +275,6 @@ struct interface_info { int is_udpsock; ssize_t (*send_packet)(struct interface_info *, struct dhcp_packet *, size_t, struct in_addr, struct sockaddr_in *, struct hardware *); -}; - -struct hardware_link { - struct hardware_link *next; - char name[IFNAMSIZ]; - struct hardware address; }; struct dhcpd_timeout {