There are a number of third-party products which integrate with ePO. The SIARevocation extension allows ePO to shut down an extension that was doing something "bad", for example exposing a vulnerability or exhibiting some other malicious behaviour.
In theory if you're not using any third-party products then you could remove it, but my recommendation would be to leave it in place.
Thanks, I will leave it in place. Just trying to look for old stuff left behind after this upgrade to 5.1.0.