t4126: fix test that happened to work due to timing

The test did "reset --hard" (where the HEAD commit has an empty
blob at path "empty") followed by "> empty", expecting that
the index does not notice the file _changed_ since git wrote
it out upon "reset" if the redirection is done quickly enough.

There was no need to do the emptying, and it gave a wrong result
if "reset --hard" happened on time T and then ">empty" happened on
the next second T+1.  This fixes it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4126-apply-empty.sh

@@ -26,7 +26,6 @@ test_expect_success setup '
 
 test_expect_success 'apply empty' '
 	git reset --hard &&
-	>empty &&
 	rm -f missing &&
 	git apply patch0 &&
 	test_cmp expect empty
@@ -34,7 +33,6 @@ test_expect_success 'apply empty' '
 
 test_expect_success 'apply --index empty' '
 	git reset --hard &&
-	>empty &&
 	rm -f missing &&
 	git apply --index patch0 &&
 	test_cmp expect empty &&
@@ -43,7 +41,6 @@ test_expect_success 'apply --index empty' '
 
 test_expect_success 'apply create' '
 	git reset --hard &&
-	>empty &&
 	rm -f missing &&
 	git apply patch1 &&
 	test_cmp expect missing
@@ -51,7 +48,6 @@ test_expect_success 'apply create' '
 
 test_expect_success 'apply --index create' '
 	git reset --hard &&
-	>empty &&
 	rm -f missing &&
 	git apply --index patch1 &&
 	test_cmp expect missing &&