RC calibration should primary do first 4 RC input channels only

there is a problem when MissionPlanner R/C calibrations changes the MIN/MAX/TRIM of channels used for servos like gimbals, flaps etc.
After discussion on the call today we think the simple rule should be:
- for copter, only calibration channels 1 to 4 and 6 (for tuning)
- for plane and rover only calibrate 1 to 4

If you want to get fancier then ideally plane would also calibrate any channel where RCn_FUNCTION=18 or 20, as those two function types (k_aileron_with_input and k_elevator_with_input) also have a corresponding input channel. All other RCn_FUNCTION types don't have an input channel, so calibrating them is actively harmful, as it breaks output servos.

The issue names no files, tests, or entry points. Start by locating Mission Planner's RC calibration flow, then trace how channel ranges are selected for copter, plane, and rover; done means only the specified input channels are calibrated without changing unrelated servo channels.

Written by the indexing model from the issue text.