Fix download report URL in ChillMainBundle export

An extra "?" was erroneously appended to the download report URL in ChillMainBundle's export feature. This update removes the extraneous character to ensure the function works as expected with the correct URL format.

src/Bundle/ChillMainBundle/Resources/public/page/export/download-export.js

@@ -12,5 +12,5 @@ window.addEventListener("DOMContentLoaded", function(e) {
     container = document.querySelector("#download_container")
   ;
 
-  download_report(export_generate_url + "?" + query.toString(), container);
+  download_report(export_generate_url + query.toString(), container);
 });