BestFirstSearch: remove unused traverseZeroCost #5089

Job	Run time
test (11, windows-latest)	9m 5s
test (11, ubuntu-latest)	7m 39s
formatting	20s
native-image (macOS-12, default)	6m 39s
test (21, windows-latest)	9m 18s
community-test (11, windows-latest)	2m 31s
test (21, ubuntu-latest)	6m 28s
native-image (ubuntu-latest, default)	3m 25s
community-test (11, ubuntu-latest)	2m 8s
native-image (ubuntu-latest, musl)	3m 52s
dockerize	0s
	51m 25s

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