sbctl should warn when people have not reset their keys properly.

[Foxboron]

Read PK and check for the Microsoft Signature List. Error and tell people to reset and/or clear Secure Boot keys if they are present.

A PK version of this function essentially:

https://github.com/Foxboron/sbctl/blob/e2f5ff665bd2641f2fcaef880de3e6044ea59421/keys.go#L275-L281