Abandon use of accelerometer for apogee detect.

Abandon use of accelerometer for apogee detect.

Integrating the accelerometer data to compute velocity worked for one rocket
flight, but additional testing shows that it doesn't work in other
airframes. Until we figure out how this should work, we'll rely on the
altimeter to detect apogee.

Signed-off-by: Keith Packard <keithp@keithp.com>