Fix Sysid filtered output

[stephendade]

As reported in https://discuss.ardupilot.org/t/how-to-set-up-separate-udp-connections-for-multiple-rovers-in-sitl-using-mavproxy/, the output sysid 1 127.0.0.1:14550 (filtering output by sysid) is broken, as it blocks further processing of MAVLink messages.

In doing this, I've removed some unused code that appears to be from the 2016 OBC.