apply tests: don't ignore "git ls-files" exit code, drop sub-shell

Fix code added in 969c877506 (git apply --directory broken for new
files, 2008-10-12) so that it doesn't invoke "git ls-files" on the
left-hand-side of a pipe, instead let's use an intermediate file.

Since we're doing that we can also drop the sub-shell that was here to
group the two.

There are a lot of these sorts of patterns in the test suite, and
there's no particular reason to fix this one other than in a preceding
commit all similar patterns except this one were fixed in
"t/t4128-apply-root.sh", so let's fix this one straggler as well.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4128-apply-root.sh

@@ -96,7 +96,8 @@ test_expect_success 'apply --directory (delete file)' '
 	echo content >some/sub/dir/delfile &&
 	git add some/sub/dir/delfile &&
 	git apply --directory=some/sub/dir/ --index patch &&
-	! (git ls-files | grep delfile)
+	git ls-files >out &&
+	! grep delfile out
 '
 
 cat > patch << 'EOF'