Remove `@context` property from CredentialObject examples

[arnoweiss]

What's wrong?

The CredentialObject example has an @context object that contains prefix-definition.

Why is this a bug?

The CredentialObject is always embedded in the issuerMetadata or CredentialOfferMessage payloads, both of which always have a mandatory @context property. While the schemas would allow for an embedded context, the spec shouldn't encourage it.

How could it be fixed?

Remove property from example

More context

Came up in the review of https://github.com/eclipse-dataspace-dcp/decentralized-claims-protocol/pull/89

[arnoweiss]

102 complicated this even more as the property is now normative in the markdown file but not in the json-schema. Approach:

• remove @context from list of required properties in md
• leave @context in imported example json and add note in md on why
• leave schema and example as-is