Rust: remove shipped feature flag #4586

Job	Run time
Diagnostic export (macos-latest, linked)	1m 58s
Diagnostic export (ubuntu-latest, linked)	1m 16s
Diagnostic export (macos-latest, nightly-latest)	1m 26s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 18s
Diagnostic export (windows-latest, linked)	2m 52s
Diagnostic export (windows-latest, nightly-latest)	4m 45s
	13m 35s

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