Removed sync group from SpeedController interface (#51)

CANJaguar is the only motor controller using sync groups, so that feature doesn't belong in an interface used by all motor controllers. If teams want to use sync groups, they should cast to the appropriate motor controller type themselves.

wpilibc/athena/src/CANTalon.cpp

@@ -132,7 +132,7 @@ float CANTalon::Get() const {
  * @param outputValue The setpoint value, as described above.
  * @see SelectProfileSlot to choose between the two sets of gains.
  */
-void CANTalon::Set(float value, uint8_t syncGroup) {
+void CANTalon::Set(float value) {
   /* feed safety helper since caller just updated our output */
   m_safetyHelper->Feed();