send-email: don't needlessly abs_path() the core.hooksPath

send-email: don't needlessly abs_path() the core.hooksPath

In c8243933c74 (git-send-email: Respect core.hooksPath setting,
2021-03-23) we started supporting core.hooksPath in "send-email". It's
been reported that on Windows[1] doing this by calling abs_path()
results in different canonicalizations of the absolute path.

This wasn't an issue in c8243933c74 itself, but was revealed by my
ea7811b37e0 (git-send-email: improve --validate error output,
2021-04-06) when we started emitting the path to the hook, which was
previously only internal to git-send-email.perl.

The just-landed 53753a37d09 (t9001-send-email.sh: fix expected
absolute paths on Windows, 2021-05-24) narrowly fixed this issue, but
I believe we can do better here. We should not be relying on whatever
changes Perl's abs_path() makes to the path "rev-parse --git-path
hooks" hands to us. Let's instead trust it, and hand it to Perl's
system() in git-send-email.perl. It will handle either a relative or
absolute path.

So let's revert most of 53753a37d09 and just have "hooks_path" return
what we get from "rev-parse" directly without modification. This has
the added benefit of making the error message friendlier in the common
case, we'll no longer print an absolute path for repository-local hook
errors.

1. http://lore.kernel.org/git/bb30fe2b-cd75-4782-24a6-08bb002a0367@kdbg.org

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