Rust: remove shipped feature flag #4695

Job	Run time
Diagnostic export (windows-latest, linked)	3m 49s
Diagnostic export (ubuntu-latest, linked)	1m 11s
Diagnostic export (windows-latest, nightly-latest)	3m 20s
Diagnostic export (macos-latest, linked)	1m 21s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 5s
Diagnostic export (macos-latest, nightly-latest)	1m 8s
	11m 54s

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