accel cal UI

some users think they need to do both of the calibration options shown here:
There are really 3 accel cal options:
- 3-axes accel cal (which most users should be doing)
- single-axis accel cal, useful for vehicles where the 3-axis is impossible, not as accurate
- calibrate just the AHRS trims, useful for when you have re-seated the flight controller in the vehicle and just want to adjust the trim

We need to make the options clearer and guide users to the full 3-axis cal as the normal cal

Start by locating the accelerometer calibration UI shown in the issue and compare its three options: 3-axis, single-axis, and AHRS-trim calibration. Done means the labels and guidance clearly identify 3-axis calibration as the normal choice and explain when the other two options are appropriate.

Written by the indexing model from the issue text.