Bug 33956: Use Koha::Biblio->opac_summary_html from opac-user.pl

Bug 33956: Use Koha::Biblio->opac_summary_html from opac-user.pl

This code is currently duplicated in controllers opac-readingrecord.pl
and opac-user.pl.

After bug 33949 it will be removed from opac-readingrecord.pl, and bug
33956 aims to remove it from opac-user.pl.

Final situation will be: we have the code in a module, covered by tests
\o/

Test plan:
Check an item out
Setup OPACMySummaryHTML ("biblionumber: {BIBLIONUMBER}" for instance)
Go to the "Your summary" at the OPAC and notice the "Links" column
Everything should work identically before and after this patch

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>