t5516: drop ok=sigpipe from unreachable-want tests

t5516: drop ok=sigpipe from unreachable-want tests

We annotated our test_must_fail calls in 8bf4becf0c (add "ok=sigpipe" to
test_must_fail and use it to fix flaky tests, 2015-11-27) because the
abrupt hangup of the server meant that we'd sometimes fail on read() and
sometimes get SIGPIPE on write().

But since 143588949c (fetch: ignore SIGPIPE during network operation,
2019-03-03), we make sure that we end up with a real die(), and our
tests no longer need to work around the race.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>