when deleting user, delete each todolist with .remove()

models/User.js

@@ -22,15 +22,10 @@ UserSchema.plugin(passportLocalMongoose);
 UserSchema.plugin(uniqueValidator);
 
 UserSchema.pre('remove', async function () {
-  await this.model('TodoList')
+  const lists = await this.model('TodoList')
     .find({ user: this._id })
-    .remove()
-    .exec();
-
-  await this.model('Todo')
-    .find({ user: this._id })
-    .remove()
     .exec();
+  await Promise.all(lists.map(list => list.remove()));
 });
 
 UserSchema.methods.generateJwt = function () {