Why tools folder is missing from missing from 5.1.1 release?

In 5.0.1 release there was “tools” folder with “denoiser_training” directory inside. But in 5.1.1 version this is missing, and I did not find a reason for this in release notes.

Is it available as separate download, or downloading old SDK is the only way to get it? If the latter, what was the latest SDK version when it was still included, 5.0.1 or 5.1.0?