See discussion here:
https://github.com/ArduPilot/ardupilot/issues/7331
we were getting some uninitialised variables. While it only showed up in
AP_SbusOut, it means we can't be sure it won't happen on other objects,
so safest to remove the approach
Thanks to assistance from Lucas, Peter and Francisco
* Retains ability to read from Analog Pin
* Adds ability to read RSSI from PWM channel value as is done in OpenLRSng, EazyUHF, and various other LRS.
* Handles any type of RSSI that provides RSSI values inverted - i.e. when the low value is the best signal and the high value is the worst signal.
* Has different key names from all existing RSSI parameters to provide for a clean break and easier distinguishing.
Peter Barker
Andrew Tridgell
Lucas De Marchi
Mathieu OTHACEHE
Randy Mackay
Stewart Loving-Gibbard