smux: remove `tick` argument from smux_trap()

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.