write_or_die: drop write_or_whine_pipe()

write_or_die: drop write_or_whine_pipe()

This function has no callers, and is not likely to gain any
because it's confusing to use.

It unconditionally complains to stderr, but _doesn't_ die.
Yet any caller which wants a "gentle" write would generally
want to suppress the error message, because presumably
they're going to write a better one, and/or try the
operation again.

And the check_pipe() call leads to confusing behaviors. It
means we die for EPIPE, but not for other errors, which is
confusing and pointless.

On top of all that, it has unusual error return semantics,
which makes it easy for callers to get it wrong.

Let's drop the function, and if somebody ever needs to
resurrect something like it, they can fix these warts.

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