The `highres_image_url` param in `card()` macro does nothing?

[alexgibson]

Description

Whilst working on https://github.com/mozilla/bedrock/issues/12019 I noticed the card() macro has a highres_image_url param. This seems to be coming from Contentful, but inspecting the macro logic itself, the param doesn't seem to be used.

Is this something only partially implemented? Do we need to keep it?

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Success Criteria

• [ ] Macro is either updated to use param, or param is removed.