tag: remove a TODO item from the test suite

tag: remove a TODO item from the test suite

Change the test for "git tag -l" to not have an associated TODO
comment saying that it should return non-zero if there's no tags.

This was added in commit ef5a6fb597 ("Add test-script for git-tag",
2007-06-28) when the tests for "tag" were initially added, but at this
point changing this would be inconsistent with how "git tag" is a
synonym for "git tag -l", and would needlessly break external code
that relies on this porcelain command.

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