Use test-lib.sh's `test_count`, instead instead of having t7900-subtree.sh do its own book-keeping with `subtree_test_count` that has to be explicitly incremented by calling `next_test`. Signed-off-by: Luke Shumaker <lukeshu@datawire.io> Signed-off-by: Junio C Hamano <gitster@pobox.com>