t3008: find test-tool through path lookup

Do not use $GIT_BUILD_DIR without quotes; it may contain spaces and be
split into fields. But it is not necessary to access test-tool with an
absolute path in the first place as it can be found via path lookup.
Remove the explicit path.

Signed-off-by: Johannes Sixt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: j6t

t/t3008-ls-files-lazy-init-name-hash.sh

@@ -4,7 +4,7 @@ test_description='Test the lazy init name hash with various folder structures'
 
 . ./test-lib.sh
 
-if test 1 -eq $($GIT_BUILD_DIR/t/helper/test-tool online-cpus)
+if test 1 -eq $(test-tool online-cpus)
 then
 	skip_all='skipping lazy-init tests, single cpu'
 	test_done