git-send-email: unconditionally use Net::{SMTP,Domain}

git-send-email: unconditionally use Net::{SMTP,Domain}

The Net::SMTP and Net::Domain were both first released with perl
v5.7.3[1], since my d48b284183 ("perl: bump the required Perl version
to 5.8 from 5.6.[21]", 2010-09-24) we've depended on 5.8, so there's
no reason to conditionally require them anymore.

This conditional loading was initially added in
87840620fd ("send-email: only 'require' instead of 'use' Net::SMTP",
2006-06-01) for Net::SMTP and 134550fe21 ("git-send-email.perl - try
to give real name of the calling host to HELO/EHLO", 2010-03-14) for
Net::Domain, both of which predate the hard dependency on 5.8.

Since they're guaranteed to be installed now let's "use" them
instead. The cost of loading them both is trivial given what
git-send-email does (~15ms on my system), and it's better to not defer
any potential loading errors until runtime.

This patch is better viewed with -w, which shows that the only change
in the last two hunks is removing the "if eval" wrapper block.

1. $ parallel 'corelist {}' ::: Net::{SMTP,Domain}
   Data for 2015-02-14
   Net::SMTP was first released with perl v5.7.3

   Data for 2015-02-14
   Net::Domain was first released with perl v5.7.3

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