Rust: remove shipped feature flag #4401

Job	Run time
Diagnostic export (macos-latest, nightly-latest)	1m 33s
Diagnostic export (ubuntu-latest, linked)	1m 8s
Diagnostic export (windows-latest, nightly-latest)	4m 42s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 7s
Diagnostic export (macos-latest, linked)	1m 3s
Diagnostic export (windows-latest, linked)	2m 50s
	12m 23s

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