Improve AppUrl/ROOT_URL checking (#22836)

After some PRs:
* #21986
* #22795
* #22808
* #22831
* #22839

Users won't be affected by the ROOT_URL problem in most cases. Close
#19345

This PR improves AppUrl/ROOT_URL checking, only check it on the admin
page, and the message is also updated.

Feel free to suggest about more English-native messages.



![image](https://user-images.githubusercontent.com/2114189/217811809-7d44ddb7-2c4a-46d0-a5db-8ae6ee65f8c3.png)

web_src/js/index.js

@@ -48,7 +48,6 @@ import {
   initCommitStatuses,
 } from './features/repo-commit.js';
 import {
-  checkAppUrl,
   initFootLanguageMenu,
   initGlobalButtonClickOnEnter,
   initGlobalButtons,
@@ -199,5 +198,4 @@ $(document).ready(() => {
   initUserAuthWebAuthnRegister();
   initUserSettings();
   initViewedCheckboxListenerFor();
-  checkAppUrl();
 });