Bug 40523: Remove unused variable from datatables.js

This change removes an unused variable from datatables.js

Test plan:
0. Apply the patch
1. Go to http://localhost:8080/cgi-bin/koha/opac-main.pl
2. Search for this payload: "abc123"
3. Click on "Search history" in the top right corner of the screen
4. Click ""CSV", "Copy", and "Print" on the "Current session" toolbar
5. Note that all the buttons work as expected

Signed-off-by: Owen Leonard <oleonard@myacpl.org>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit b572ae29eb)
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>

koha-tmpl/opac-tmpl/bootstrap/js/datatables.js

@@ -428,37 +428,6 @@ function _dt_buttons(params) {
         },
     };
 
-    var export_buttons = [
-        {
-            extend: "excelHtml5",
-            exportOptions: {
-                columns: exportColumns,
-                format: export_format,
-            },
-        },
-        {
-            extend: "csvHtml5",
-            exportOptions: {
-                columns: exportColumns,
-                format: export_format,
-            },
-        },
-        {
-            extend: "copyHtml5",
-            exportOptions: {
-                columns: exportColumns,
-                format: export_format,
-            },
-        },
-        {
-            extend: "print",
-            exportOptions: {
-                columns: exportColumns,
-                format: export_format,
-            },
-        },
-    ];
-
     let buttons = [
         {
             fade: 100,