model: should we remove "access" and "repository" for now?

I think we would be better to start with smaller, more manageable metadata record for dandiset, without hard-coding things such as `repository` and `access` (seems to be also a tricky one: #343 ). It would always be easier to extend, or to provide custom mapping (e.g. based on identifier being DANDI we could make claims on `repository` and even `access`). WDYT @satra?

edit 1: I somewhat also dislike them since they are "the defaults" for any `DandiMeta` (which might not even yet was considered to be uploaded to the archive's metadata record).

edit 2: Actually - may be they are ok IF dandi-api server would populate them since it is not client's job since we do not upload dandiset metadata (although #341 is coming to facilitate migration). But first let's figure out #343 and then file an issue or PR for dandi-api to complement https://github.com/dandi/dandi-api/issues/64 and https://github.com/dandi/dandi-api/issues/63