Improve to unlinkability/privacy requirements around status_uri

[jogu]

HAIP currently says:

Each Credential MUST have its own unique, unpredictable status list index, even when multiple Credentials reference the same status list URI

But unique status list URIs are a privacy issue, so I think that 'even when' needs a little massaging.

[c2bo]

Should we just point to the privacy considerations of Status List here? I believe they are pretty extensive on those points.