Delete ignored Cargo.lock file

[alexrutar]

The file Cargo.lock is already (correctly) ignored in the .gitignore but the file is still present in master; this PR just deletes the file.

[a-kenji]

The file Cargo.lock is already (correctly) ignored

I just want to note that whether to add the Cargo.lock file is an opinion of the project based on their needs and there is no strict correct way:

• https://doc.rust-lang.org/cargo/faq.html#why-have-cargolock-in-version-control

That being said if a project like nucleo does ignore the lock file then it is likely they for them decided against using it.