It looks like some code was shuffled around in revision 1.34 in which snmpe_application was renamed to smi_application and this prototype was missed.
ok? Index: snmpe.c =================================================================== RCS file: /cvs/src/usr.sbin/snmpd/snmpe.c,v retrieving revision 1.52 diff -u -p -r1.52 snmpe.c --- snmpe.c 15 Apr 2018 11:57:29 -0000 1.52 +++ snmpe.c 23 Jul 2018 19:32:40 -0000 @@ -45,8 +45,6 @@ int snmpe_parse(struct snmp_message *); void snmpe_tryparse(int, struct snmp_message *); int snmpe_parsevarbinds(struct snmp_message *); void snmpe_response(struct snmp_message *); -unsigned long - snmpe_application(struct ber_element *); void snmpe_sig_handler(int sig, short, void *); int snmpe_dispatch_parent(int, struct privsep_proc *, struct imsg *); int snmpe_bind(struct address *);