archive-tar: don't reload default config options

archive-tar: don't reload default config options

We load our own tar-specific config, and then chain to
git_default_config. This is pointless, as our caller should
already have loaded the default config. It also introduces a
needless inconsistency with the zip archiver, which does not
look at the config files at all (and therefore relies on the
caller to have loaded config).

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