core: use moment-timezone

packages/hydrooj/src/libs.ts

@@ -1,8 +1,5 @@
 import AdmZip from 'adm-zip';
-import fs from 'fs-extra';
-import yaml from 'js-yaml';
 import _ from 'lodash';
-import moment from 'moment-timezone';
 import Schema from 'schemastery';
 import superagent from 'superagent';
 import { Context } from './context';
@@ -12,7 +9,7 @@ export * from './utils';
 export * from './interface';
 export * from './typeutils';
 export {
-    Schema, yaml, fs, AdmZip, superagent, _, moment,
+    Schema, AdmZip, superagent, _,
 };
 export const definePlugin = <T = never>(args: {
     using?: keyof Context[];