Remove spec text: "... Messages MUST be committed to an IPLD DAG in a tree allocated to the DID of the owner ..."

> In order to enable data replication features for a [Decentralized Web Node](https://identity.foundation/decentralized-web-node/spec/#term:decentralized-web-node), all Messages MUST be committed to an IPLD DAG in a tree allocated to the DID of the owner after all subtrees are composed and committed. The top-level of Message objects MUST be committed as a [DAG CBOR](https://github.com/ipld/specs/blob/master/block-layer/codecs/dag-cbor.md) encoded object.

The above text is outdated especially the first sentence. The word "committed" is ambiguous in "... MUST be committed as a DAG CBOR", I read it as "it must be stored as DAG CBOR", but that's not cace, we only use IPLD DAG CBOR/PB for generating CIDs.

We need to update or remove this text.