Remove statefulness of pre-approved witness DID log

[brianorwhatever]

As noted here I don't love that we're holding onto this pending state somewhere. As noted in that comment these are the ideas I came up with

• /.well-known/pending-did.jsonl being the log in it's pending state
• allowing the DID controller to update their did.jsonl with the pending state as the last entry, and specifying how a resolver would interpret this state (ie fallback to previous version unless a param was included)
• specifying they need to remember this pending state

[swcurran]

Action: Leave in the spec -- consider clarifying why that is done. @swcurran

[swcurran]

Reviewed the spec and I think this is clear (although there is markdown error -- I'll fix that).

Closing this issue.