RC_Channel: Removed duplicate defines from RC_Channel.h
Tools/AntennaTracker: removed duplicate update_tracker from task list
Tools/AntennaTracker: completed intial tracker code

Now works with 2 servo alt-azimuth mounted antenna tracking mount. Tested
on Flymaple, with Eagle Tree antenna tracker.
Tools/AntennaTracker: remove redundant comment
autotest: sim_arduplane.sh works with a range of terminal types
Rover: only send GPS2_RAW when we have a 2nd GPS
Copter: only send GPS2_RAW when we have a 2nd GPS
Plane: only send GPS2_RAW when we have a 2nd GPS
autotest: use xterm by default and only use make clean if needed
SITL: added SIM_GPS2_ENABLE option
HAL_SITL: honor SIM_GPS2_ENABLE option