Use test_might_fail instead of ignoring the exit status from git
config --unset, and let the exit status propagate past rm -f (which
does not fail on ENOENT). Otherwise bugs that lead git config to
crash would not be detected when this test runs.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>