Auto merge of #11662 - epage:docs, r=ehuss

docs(contrib): Remove out-of-date process step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.

src/doc/contrib/src/process/unstable.md

@@ -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
 
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