t1600-index: remove unnecessary redirection

In a helper function in the 't1600-index.sh' test script the stderr
of a 'git add' command is redirected to its stdout, but its stdout is
not redirected anywhere.  So apparently this redirection is
unnecessary, remove it.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1600-index.sh

@@ -79,7 +79,7 @@ test_index_version () {
 		else
 			unset GIT_INDEX_VERSION
 		fi &&
-		git add a 2>&1 &&
+		git add a &&
 		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual