Bug 21501: Remove dead code from course reserves module
search_on parameter is not used in any templates so course-reserves.pl
can be simplified a bit
Test plan:
1. Go to course reserves module and verify that it is still working
2. `git grep search_on` should return nothing
Signed-off-by: Pierre-Marc Thibault <pierre-marc.thibault@inLibro.com> Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org> Signed-off-by: Nick Clemens <nick@bywatersolutions.com>