Rust: remove shipped feature flag #5232

Job	Run time
Ruby analysis (ubuntu-latest, default)	1m 0s
Ruby analysis (macos-latest, linked)	1m 9s
Ruby analysis (macos-latest, nightly-latest)	1m 43s
Ruby analysis (macos-latest, default)	1m 19s
Ruby analysis (ubuntu-latest, nightly-latest)	1m 9s
Ruby analysis (ubuntu-latest, linked)	1m 0s
	7m 20s

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