Rust: remove shipped feature flag #7394

Job	Run time
Split workflow (macos-latest, linked)	1m 18s
Split workflow (ubuntu-latest, linked)	1m 15s
Split workflow (macos-latest, default)	1m 15s
Split workflow (ubuntu-latest, default)	1m 19s
Split workflow (ubuntu-latest, nightly-latest)	1m 26s
Split workflow (macos-latest, nightly-latest)	1m 37s
	8m 10s

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