Defining CID without Multibase prefix

[vmx]

In the current version of the spec a CID is defined as containing a multibase prefix.

This doesn't align with the current understanding across the IPLD team. We regard a CID as <cid-version><ipld-codec><multihash>. In cases where a CID is not represented as bytes (e.g. for display purpose) it is Multibase encoded.