Rust: remove shipped feature flag #4585

Job	Run time
Diagnostic export (windows-latest, linked)	3m 18s
Diagnostic export (macos-latest, linked)	2m 2s
Diagnostic export (macos-latest, nightly-latest)	2m 5s
Diagnostic export (ubuntu-latest, linked)	1m 25s
Diagnostic export (windows-latest, nightly-latest)	3m 21s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 16s
	13m 27s

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