[lint] Fix some clippy warnings on Cargo manifests

[woshilapin]

clippy::cargo is not enabled by default but can provide some useful hints on Cargo.toml manifests. However, there is no easy way to solve the problem of multiple versions of dependencies so I specifically deactivated this one.

[datanel]

cargo:clippy includes

• cargo_common_metadata (what you changed in this PR)
• multiple_crate_versions (excluded in your PR)
• wildcard_dependencies (I think we will never include "*" as version)

Now that you applied all the recommandations from cargo_common_metadata, is it useful to always check clippy::cargo ?
May be if we add a new "sub-crate". I don't see well the benefice.

[woshilapin]

Now that you applied all the recommandations from cargo_common_metadata, is it useful to always check clippy::cargo ?

I would say yes, for the same reasons that we didn't remove clippy in general even if we already fixed all the warnings and errors (I agree changes on Cargo.toml are much less frequent but still).

May be if we add a new "sub-crate". I don't see well the benefice.

A few reasons to keep it, in my opinion:

• new developers might come in, not necessarily aware of all our practices
• new sub-crates might be created
• new clippy::cargo rules might appears (today, only 3 but more might be created)