Fix permission issue DigitalCredentials API on iOS

[davidz25]

We currently try to remove all registrations which fails on the first run after install because the app lacks permission. This can be worked around by the user manually granting permission in the iOS Settings app. The solution here is likely to record in DocumentStore which documents are already registered and don't attempt to remove registrations for things we never registered.

[davidz25]

This should be fixed before releasing 0.97.0