Copter: remove DRIFT and SPORT from manual_flight_mode function

ArduCopter/flight_mode.pde

@@ -259,8 +259,6 @@ static bool manual_flight_mode(uint8_t mode) {
     switch(mode) {
         case ACRO:
         case STABILIZE:
-        case DRIFT:
-        case SPORT:
             return true;
         default:
             return false;