core: delete task when deleting contest

packages/hydrooj/package.json

@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.1.37",
+    "version": "3.1.38",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",

packages/hydrooj/src/handler/contest.ts

@@ -116,6 +116,9 @@ export class ContestDetailHandler extends Handler {
         const tdoc = await contest.get(domainId, tid);
         if (!this.user.own(tdoc)) this.checkPerm(PERM.PERM_EDIT_CONTEST);
         await contest.del(domainId, tid);
+        await TaskModel.deleteMany({
+            type: 'schedule', subType: 'contest.problemHide', domainId, tid,
+        });
         this.response.redirect = this.url('contest_main');
     }
 }