Remove `artifact_v4_upgrade` feature flag logic and related PR checks #6064

Job	Run time
Packaging: Action input (ubuntu-latest, linked)	1m 24s
Packaging: Action input (macos-latest, linked)	1m 37s
Packaging: Action input (windows-latest, linked)	6m 34s
Packaging: Action input (ubuntu-latest, default)	1m 10s
Packaging: Action input (macos-latest, default)	2m 29s
Packaging: Action input (windows-latest, default)	6m 34s
Packaging: Action input (ubuntu-latest, nightly-latest)	1m 23s
Packaging: Action input (macos-latest, nightly-latest)	2m 15s
Packaging: Action input (windows-latest, nightly-latest)	9m 0s
	32m 26s

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