altos: Stop storing pyro fired status in config block

altos: Stop storing pyro fired status in config block

We already have the fired status saved in the ao_pyro_fired variable,
so just use that to detect whether a channel has already been fired.

Fixes possible cases where the pyro config data gets written back to
eeprom with the fired bit set, which then inhibits the channel during
flight.

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