Improve handling of unregistered files at uninstall #1284

Job	Run time
build_NetCore (Debug_NetCore)	1m 8s
build_NetCore (Release_NetCore)	1m 1s
build (6.8, Debug)	1m 25s
build (6.8, Release)	2m 27s
build (6.10, Debug)	1m 25s
build (6.10, Release)	1m 18s
build (6.12, Debug)	1m 28s
build (6.12, Release)	1m 42s
build (latest, Debug)	1m 26s
build (latest, Release)	2m 0s
	15m 20s

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