Deprecate single-arg signal KIdleTime::timeoutReached(int identifier)

Being an overload to the signal with the additional int msec argument, connecting to it using a memberfunction pointer requires to specifcy for the compiler which overload to use (e.g. with QOverload<>). Instead of renaming one of the signals, the overload with less arguments is dropped, as the multi-arg signal can be used for that need as well, igoring the second argument for the slot.