Review unused dependencies

[josecelano]

$ cargo +nightly udeps --all-targets
unused dependencies:
`torrust-tracker v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker)`
└─── dependencies
     └─── "hex"
`torrust-tracker-configuration v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/configuration)`
└─── dependencies
     └─── "uuid"
`torrust-tracker-located-error v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/located-error)`
└─── dependencies
     └─── "thiserror"
`torrust-tracker-test-helpers v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/test-helpers)`
└─── dependencies
     └─── "tokio"
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.

Originally posted by @josecelano in #212 (comment)

[josecelano]

Updated command output:

unused dependencies:
`torrust-tracker v3.0.0-alpha.1 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker)`
└─── dependencies
     ├─── "hex"
     └─── "toml"
`torrust-tracker-configuration v3.0.0-alpha.1 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/configuration)`
└─── dependencies
     └─── "uuid"
`torrust-tracker-located-error v3.0.0-alpha.1 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/located-error)`
└─── dependencies
     └─── "thiserror"
`torrust-tracker-test-helpers v3.0.0-alpha.1 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/test-helpers)`
└─── dependencies
     └─── "tokio"
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.