Remove query diffing entirely

[stubailo]

As discussed in #615

It does indeed simplify the code significantly!

TODO:

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change
• Add your name and email to the AUTHORS file (optional)

[stubailo]

Pretty confused about these test failures, I might be missing something big. Or perhaps there's a one line fix that gets them all.

[stubailo]

@helfer can you review please?

[helfer]

Some changes seem unrelated to the PR (eg. concurrently and dataloader in package.json), but lgtm otherwise.