daemon.c: refactor hostinfo_init() to HOSTINFO_INIT macro

daemon.c: refactor hostinfo_init() to HOSTINFO_INIT macro

Remove the hostinfo_init() function added in 01cec54e135 (daemon:
deglobalize hostname information, 2015-03-07) and instead initialize
the "struct hostinfo" with a macro.

This is the more idiomatic pattern in the codebase, and doesn't leave
us wondering when we see the *_init() function if this struct needs
more complex initialization than a macro can provide.

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