Change the coverage-report target so that it doesn't generate the
coverage-untested-functions file by default. I'm adding more targets
for doing various things with the gcov files, and they shouldn't all
run by default.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>