Update Rust dependencies

[tjkirch]

Description of changes:

b1614643 tools: cargo update

2ea330cc Update semver to 1.0
    This has to be done in the tools and sources workspaces simultaneously because
    of the updater dependency in pubsys.
    
    The semver parser changed, so some version values we considered "good" before
    (but didn't actually use) now fail to parse, and so were moved to the "bad"
    value unit test.

b5406bdb sources: cargo update
7b52c7de apiserver: update for actix-web 4.0.0-beta.6
af64e03d sources: update nix to 0.21
3279c077 sources: update darling
bf90d364 imdsclient: remove unused simplelog dependency
e8c95b66 ecs-settings-applier: remove unused model dependency

Not updated:

• gptman
• hyper (in sources/)
• handlebars - lots of template breakage; we could adapt our templates to it, but they wouldn't look right, so I think it's better to wait for a resolution to that issue.

Big thanks to @webern for helping figure out the apiserver changes for actix 4.0.0-beta.6, and the issue with handlebars.

Testing done:

Unit tests pass. Built k8s and ECS AMIs. Confirmed systemctl status running, dmesg and journal OK. Ran a pod/task OK. Made API changes OK.

Confirmed that the API still returns our custom error codes and messages, after the changes required for actix.

Confirmed that cargo make repo and cargo make ssm still work OK.

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.

[tjkirch]

(Sorry, didn't mean to assign reviewers yet. Testing should be done soon.)

[tjkirch]

Testing looked good, setting as ready for review.

[tjkirch]

I'm doing another quick cargo update of sources and tools to get the tokio 1.7.1 bugfix which might be important. Update coming soon.

[tjkirch]

^ This push updates tokio, globset, and rustc-demangle (used by backtrace, in turn used by snafu) in the sources and tools crates. I didn't do a full cargo update because there was another backwards-incompatible actix beta release over the weekend and I don't want to bring in more changes right now.

Unit tests still pass, and I reconfirmed the above testing with an x86 aws-k8s-1.20 AMI.