Fixed the HIL actuator range to what it should be

@DrTon @julianoes @thomasgubler The HIL actuator outputs were scaled incorrectly with respect to the message spec:
https://pixhawk.ethz.ch/mavlink/#HIL_CONTROLS

I'm guessing this was an adjustment for multicopters. However, the SIM of a multicopter should also obey this range:

0% throttle: -1, 100% throttle: +1. Note that this is the *normalized actuator range* (post-mixer), not the *normalized controls range* (pre-mixer).