Bug 12478: Define simple_search_compat for Zebra

Bug 12478: Define simple_search_compat for Zebra

When Zebra is defined as the search engine, the authority search is
broken (Can't locate object method "simple_search_compat" via package
"Koha::SearchEngine::Zebra::Search" at /home/koha/koha/C4/AuthoritiesMarc.pm line 357.)
simple_search_compat is not defined in
Koha::SearchEngine::Zebra::Search, it should be a wrapper for
C4::Search::SimpleSearch

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jesse Weaver <jweaver@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>