Disable debug output.
Only set OK-to-arm flag when arm switches are disabled.

This prevents arming after connecting a battery when the throttle is in
low; when using a switch to arm and when the switch is left in the ON
position.

The previous solution was flawed because of the way rc input is handled.

This also removes an extra test of rcOptions by re-arranging the logic
that handles arming/disarming via a switch.