Fix unused key issue in zh-HK (#2870)

* locale: remove unused keys in zh-HK

* locale: update json translations

* handled the untranslated strings.
* removed unused keys.

app/javascript/mastodon/locales/whitelist_zh-HK.json

@@ -1,2 +1,3 @@
 [
+  "getting_started.support"
 ]

app/javascript/mastodon/locales/zh-HK.json

@@ -60,12 +60,12 @@
   "empty_column.public": "跨站時間軸暫時沒有內容！快寫一些公共的文章，或者關注另一些服務站的用戶吧！你和本站、友站的交流，將決定這裏出現的內容。",
   "follow_request.authorize": "批准",
   "follow_request.reject": "拒絕",
-  "getting_started.appsshort": "Apps",
-  "getting_started.faq": "FAQ",
+  "getting_started.appsshort": "手機應用",
+  "getting_started.faq": "常見問題",
   "getting_started.heading": "開始使用",
   "getting_started.open_source_notice": "Mastodon（萬象）是一個開放源碼的軟件。你可以在官方 GitHub ({github}) 貢獻或者回報問題。",
   "getting_started.support": "{faq} • {userguide} • {apps}",
-  "getting_started.userguide": "User Guide",
+  "getting_started.userguide": "使用指南",
   "home.column_settings.advanced": "進階",
   "home.column_settings.basic": "基本",
   "home.column_settings.filter_regex": "使用正規表達式 (regular expression) 過濾",