smux: remove `tick` argument from smux_trap()

smux_trap() contains an argument whose use appears to be to set
sysUpTime.0/timestamp field in SNMP trap. However, this value is not
used in smux_trap(). Moreover, it is expected that this field is the
value of sysUpTime.0 when the trap was sent and not any other time
related to the trap. To avoid any confusion, we remove this field from
the signature of the function.
diff --git a/lib/agentx.c b/lib/agentx.c
index 9cf6de5..2358581 100644
--- a/lib/agentx.c
+++ b/lib/agentx.c
@@ -125,7 +125,7 @@
 smux_trap (const oid *name, size_t namelen,
 	   const oid *iname, size_t inamelen,
 	   const struct trap_object *trapobj, size_t trapobjlen,
-	   unsigned int tick, u_char sptrap)
+	   u_char sptrap)
 {
   return 1;
 }