Bug 14351: Remove given-when from opac-search.pl

Bug 14351: Remove given-when from opac-search.pl

Reformats given-when to if-elsif-else in opac-search.pl
to remove the experimental feature and with it a lot
of warnings from the logs.

To test:
- Do several different advanced searches with and
  without expanded search options
- Verify the link back to the search appears above
  the results list and works correctly

See also: test plan on bug 13307

NOTE: Even installed firefox plug in to edit cookies to
      trigger else case. :)

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>