Clean up dependencies

[mkatychev]

Handle dependabot warnings: https://github.com/knox-networks/ssi/security/dependabot/7

• Removed unused dependencies with cargo-udeps:

  $ cargo +nightly udeps --all-targets
  
  unused dependencies:
  `ssi-ffi v0.4.0 (/Users/mkatychev/Documents/knox/ssi/ffi)`
  └─── dependencies
     └─── "ephemeral_resolver"
  `ssi_core v0.4.0 (/Users/mkatychev/Documents/knox/ssi/core)`
  └─── dev-dependencies
     ├─── "async-std"
     └─── "map"
  Note: They might be false-positive.
      For example, `cargo-udeps` cannot detect usage of crates that are only used in doc-tests.
      To ignore some dependencies, write `package.metadata.cargo-udeps.ignore` in Cargo.toml.
  

• Run cargo upgrade

[mkatychev]

@LuisOsta are you talking about https://docs.rs/signature/latest/signature/ or the workspace crate? because crates.io/signature has not been updated

[LuisOsta]

@mkatychev I'm talking about the workspace crate signature

[LuisOsta]

Specifically ed25519-zebra and sha2 were updated