t/t7008-grep-binary.sh: un-TODO a test that needs REG_STARTEND

t/t7008-grep-binary.sh: un-TODO a test that needs REG_STARTEND

Now that we have a regex engine that supports REG_STARTEND this test
should fail if "git grep" can't grep NULL characters.

Platforms that don't have a POSIX regex engine which supports
REG_STARTEND should always define NO_REGEX=YesPlease when compiling.

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