Cargo.toml cleanups

[nnethercote]

Best reviewed one commit at a time.

The first two commits are about not repeating information. (Nb: why isn't mctp-usb-embassy part of the workspace?)

The third commit addresses a pet peeve of mine, one that not everyone shares.

[mkj]

Thanks for those cleanups!
mctp-usb-embassy is out of the workspace since it failed building it with serde std feature enabled (pulled in via mctp-standalone) via ssmarshal (a dependency of usb-embassy).
https://gitlab.com/robigalia/ssmarshal/-/issues/5

    Checking ssmarshal v1.0.0
error[E0277]: the trait bound `Error: StdError` is not satisfied
   --> /home/matt/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ssmarshal-1.0.0/src/lib.rs:64:27
    |
64  | impl serde::de::Error for Error {
    |                           ^^^^^ the trait `StdError` is not implemented for `Error`
    |
note: required by a bound in `serde::de::Error`
   --> /home/matt/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/serde-1.0.197/src/de/mod.rs:301:1

Looking again now though, we can disable the unused usbd-hid feature of usb-embassy and then it won't pull in ssmarshal. I'll give that a try.