message: docs(contrib): Remove out-of-date process step
  The `-Z` flag seems to now be documented as part of defining the feature in
  `features.rs`, so (1) the destination is wrong and (2) this will be done
  naturally as part of creating the feature.
diff: @@ -24,11 +24,7 @@ been passed.
  Every unstable feature should have a section added to the [unstable chapter]
  describing how to use the feature.
  -`-Z` CLI flags should be documented in the built-in help in the [`cli`
  -module].
  -
  [unstable chapter]: https://github.com/rust-lang/cargo/blob/master/src/doc/src/reference/unstable.md
  -[`cli` module]: https://github.com/rust-lang/cargo/blob/master/src/bin/cargo/cli.rs
  ## Tracking issues
  