Revert fix(wasapi): do not emit DeviceChanged when not rerouted

[LastExceed]

This reverts commit e7d920b.

Closes #1339

[roderickvd]

This seems to throw out more than #1339 needs. StreamInvalidated is wrong when a replacement device exists, but default_device_change_error's other branch serves a different purpose:

OnDeviceStateChanged and OnDeviceRemoved only SetEvent when get_current_default(self.flow).is_none() (see the comment above them), so they only ever wake this code up for the no-replacement case. After this revert that case gets reported as DeviceChanged too, which contradicts its definition: "the stream remains active and no rebuild is required." There's nothing to route to there, so that isn't true.

I think the fix should be smaller than a full revert: keep default_device_change_error, just fix the one arm that was actually wrong:

fn default_device_change_error(flow: Option<Audio::EDataFlow>) -> Error {
    match flow.and_then(get_current_default) {
        None => ErrorKind::DeviceNotAvailable.into(),
        Some(_) => ErrorKind::DeviceChanged.into(), // was StreamInvalidated
    }
}

[roderickvd]

I think this should be a bit more succinct: just document observable behavior, no need to pony up about being wrong or right.