Remove duplicate object keys

These serve no purpose except to confuse you, and make my IDE draw some
red wiggly underlines.

src/UI/UIWindowDownloadProgress.js

@@ -47,7 +47,6 @@ async function UIWindowDownloadProgress(options){
         uid: null,
         is_dir: false,
         body_content: h,
-        draggable_body: false,
         has_head: false,
         selectable_body: false,
         draggable_body: true,