Drop support for datasets V1 (except for upgrade)

[olsen232]

Note that this PR comes in two commits -

• the first part simply removes or upgrades all tests that rely on V1 datasets working properly:

  • for tests which come in pairs, with a V1 and a V2 variant, the V1 variant is simply removed
  • for a test which currently only tests against a V1 repo, it is modified to test against a V2 repo

  This part took a lot of small changes, but isn't very exciting.

• the second part actually drops support for V1 - trying to run any command except for
  sno upgrade or sno data version on a V1 repo, will simply cause an error message to be displayed:

  Sno repo uses Datasets v1, which is no longer supported.
  The latest version is v2. Use `sno upgrade SOURCE DEST` to upgrade this repo.
  

  This part also has lots of small changes, and is also not very exciting, but probably more worth your time.

Checklist:!

• Have you reviewed your own change?
• Have you included test(s)?
• Have you updated the changelog?

[craigds]

🚀 nice work