Rust: remove shipped feature flag #7404

Job	Run time
Split workflow (ubuntu-latest, linked)	1m 24s
Split workflow (macos-latest, linked)	1m 23s
Split workflow (macos-latest, default)	1m 22s
Split workflow (ubuntu-latest, default)	1m 13s
Split workflow (ubuntu-latest, nightly-latest)	1m 25s
Split workflow (macos-latest, nightly-latest)	1m 35s
	8m 22s

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