Bug 2616: Remove unnecessary 'use HTML::Template' calls

Bug 2616: Remove unnecessary 'use HTML::Template' calls

Removes deprecated calls to HTML::Template or HTML::Template::Pro from:
C4/Output.pm
catalogue/export.pl
reports/issues_by_borrower_category.plugin
reports/itemtypes.plugin

Only remaining calls are in misc/cronjobs/rss/rss.pl, misc/cronjobs/smsoverdues.pl,
and t/test_template.pl.  These scripts still legitimately depend on H:T:P

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>