fix(deps): Remove unused dependencies, and check for them in CI

[teor2345]

Motivation

Having unused dependencies makes Zebra less secure. It also increases build time and binary size.

We deleted a lot of code recently, but we didn't delete the dependencies that were only used by that code. We also copy-pasted some dependencies that weren't actually needed.

Closes #6215

Complex Code or Requirements

This has a bit of shell script in it, but it doesn't do anything unusual.

Solution

• remove unused dependencies detected by cargo-machete
• add a CI job to detect unused dependencies
  • add a patch workflow so we can make this job part of the branch protection rules

This PR should appear in the changelog because it removes dependencies, which is visible to users.

Review

This is a low priority change. It can go in after the release.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

Follow Up Work

After this PR merges, an admin should make the new job part of the branch protection rules.

[teor2345]

This seems to work:

-- full cargo machete output, including ignored dependencies --
Analyzing dependencies of crates in this directory...
 INFO  cargo_machete > /home/runner/work/zebra/zebra/Cargo.toml is a virtual manifest for a workspace
cargo-machete found the following unused dependencies in /home/runner/work/zebra/zebra:
Done!
zebra-test -- /home/runner/work/zebra/zebra/zebra-test/Cargo.toml:
	tinyvec
zebra-network -- /home/runner/work/zebra/zebra/zebra-network/Cargo.toml:
	humantime-serde
zebrad -- /home/runner/work/zebra/zebra/zebrad/Cargo.toml:
	gumdrop
	humantime-serde
	tinyvec
zebra-utils -- /home/runner/work/zebra/zebra/zebra-utils/Cargo.toml:
	tinyvec
-- unused dependencies are below this line, full output is above --
No unused dependencies found.

https://github.com/ZcashFoundation/zebra/actions/runs/4260322630/jobs/7413377013#step:5:20

[codecov]

Codecov Report

Merging #6216 (ee5f3d3) into main (84d0346) will increase coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6216      +/-   ##
==========================================
+ Coverage   77.94%   77.97%   +0.03%     
==========================================
  Files         304      304              
  Lines       39349    39349              
==========================================
+ Hits        30672    30684      +12     
+ Misses       8677     8665      -12     

[arya2]

Looks good! Thank you!