`cargo upgrade` command is not exists

[awkr]

As the pic says, in the latest Cargo, there is no upgrade subcommand. So maybe we need to remove the cargo-upgrade action to keep up with the Cargo, and make cargo.el more compact.

$ cargo --version
cargo 1.42.0 (86334295e 2020-01-31)

[kwrooijen]

Maybe we can add the upgrade, and mark update as obsolete? Since some people might still be on the older version?

[awkr]

Maybe we can add the upgrade, and mark update as obsolete? Since some people might still be on the older version?

Yeah, sounds like a better solution by taking care of more end users. Also, to make the package more concise, besides marking as obsolete, can also tell users that useless action will be removed in the next two releases.