Fix FindTurnTimeConstant rotational velocity units

[Gabe-Mitnick]

getRate() is supposed to be degrees per second, we thought it was really radians per second, turns out it's neither. probably use getRawGyroZ() instead. you could just change the variable names so they don't make it seem like the units are radians per second, since the code basically works using getRate(), but then if they release a fix to the getRate() bug, we have to change the code.