Remove project dependency support from Rust additional_dependencies

[j178]

Rust additional_dependencies currently supports two different semantics: cli:<crate> installs a CLI crate with cargo install, while non-cli: entries are treated as project dependencies and injected into the hook project via cargo add and a rebuild. That second behavior is not a good fit for prek; Rust additional_dependencies should only support CLI dependencies, and project/library dependencies should be owned by the hook repository itself in Cargo.toml and Cargo.lock.