Update Rust dependencies

[tjkirch]

Description of changes:

b5fe2438 Update Rust dependencies in tools/
c1b02559 Remove no-longer-used 'rand' dep from update_metadata
7449ff6a Remove unused 'migrator' dep from updog
7106cc70 Remove no-longer-used 'futures' dep from apiclient
01248d2d Update Rust dependencies in sources/

Perhaps the most notable update is nix, since they marked fork unsafe. In reality, it was already unsafe, because fork(2) is unsafe itself in some situations, and nix is a slim wrapper. It makes no practical difference to us other than needing an unsafe { } block - we're only using it to separate thar-be-updates from its parent process, and there's no threading.

actix-web had a major version bump, but not much changed really. Mostly stability improvements and simplification.

Things not updated:

• tokio 0.3 - hyper hasn't updated yet; you can't use old hyper in new tokio apps, at least not without hacks.
• gptman - there are big changes that need thought so as to not break our disk handling, but it has the potential to fix our "second" partition resize.
• tough - the changes in 0.9 are partially undone in 0.10, and it's not worth canceling out the work in tough: update to v0.10.0 #1190, which will handle this update.

Testing done:

• Unit tests pass
• apiserver, storewolf, settings-commiter, and apiclient tested locally through settings gets/changes/commits
• cargo make ami, cargo make repo, cargo make ssm OK
• Made AMIs for all 6 variants on x86, and aws-k8s-1.17 on aarch64, and confirmed I could run pods/tasks/containers, all boot services were healthy, journal looks OK, API working OK, etc.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[zmrow]

💸