Simplify flight_control #147
Description
The flight_control package was designed for multiple message "authors" sending descriptive PixhawkInstruction messages, which then got multiplexed and translated to bare RC In messages. We're using ManualControl messages now, and the controller is the only message author.
Remove unnecessary nodes in flight_control and make the number of nodes in the chain from the controller to the robot shorter. Remove PixhawkInstruction entirely.