Welcome,
Sorry, there is no link or support for using an older version. The older version of OpenEars wasn’t less sensitive to background noise (there are actually many older discussions in these forums about how to reduce its noise sensitivity), it just had a (very slightly) higher voice activity threshold setting, but which couldn’t be adjusted.
You can raise vadThreshold in OpenEars 2.x in order to get the same results, but also have the flexibility to set it to your usage scenario’s ideal setting. There is more info in the FAQ and 2.x-related posts in the forums about using vadThreshold and/or possibly Rejecto to ameliorate non-speech and out-of-vocabulary input.