Revert "临时禁止离线考试试卷预览"

This reverts commit 3b220b023b1a0667f0b8c102979248bddaa60b85.

src/features/OfflineExam/OfflineExamList.vue

@@ -131,11 +131,11 @@ export default {
         isOnlineExam: true
       };
       window.name = JSON.stringify(user);
-      // window.location.href =
-      //   this.tk_server_url +
-      //   "/admin/preview_paper/" +
-      //   course.paperId +
-      //   "?isback=true";
+      window.location.href =
+        this.tk_server_url +
+        "/admin/preview_paper/" +
+        course.paperId +
+        "?isback=true";
     },
     downloadOfflineFile(url) {
       window._hmt.push(["_trackEvent", "离线考试页面", "下载作答"]);