Rust: remove shipped feature flag #4693

Job	Run time
Diagnostic export (macos-latest, linked)	1m 3s
Diagnostic export (windows-latest, linked)	3m 27s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 9s
Diagnostic export (ubuntu-latest, linked)	1m 5s
Diagnostic export (macos-latest, nightly-latest)	1m 23s
Diagnostic export (windows-latest, nightly-latest)	2m 53s
	11m 0s

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