bug 3314: remove disused scripts and API functions

bug 3314: remove disused scripts and API functions

The distributedto column of the subscription table is
no longer used, having been replaced by the serials
routing list table.  This patch removes two C4::Serials
functions and a script and template, none of which were
reachable by current code:

C4::Serials::GetDistributedTo()
C4::Serials::SetDistributedTo()
koha-tmpl/intranet-tmpl/prog/en/modules/serials/distributedto.tmpl
serials/distributedto.pl

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>