Bug 19767: Remove unused serial-issues.pl script

Bug 19767: Remove unused serial-issues.pl script

This patch removes three unused files:

serials/serial-issues.pl

...and its associated templates:

koha-tmpl/intranet-tmpl/prog/en/modules/serials/serial-issues-full.tt
koha-tmpl/intranet-tmpl/prog/en/modules/serials/serial-issues.tt

To test, apply the patch and search the Koha codebase for references to
any of those files. None should exist.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>