[JENKINS-26520] Documentation fix for $BUILD_ID

prevent removing artifact when build isn’t completed yet

Without this change you need to do:

```
User user;
final SecurityContext oldContext = ACL.impersonate(a);
try {
    user = User.current();
} finally {
    SecurityContextHolder.setContext(oldContext);
}
```

Which seems incredibly wasteful.

Or else you need to replicate the logic in User.current() which makes that code hard to change.

[FIXED JENKINS-26208] Do not skip polling while quieting down

[JENKINS-27414] Don't offer to restart if unsupported

[FIXED JENKINS-26751] Do not run /script on offline slave

[FIXED JENKINS-21322] Configure periodic ws cleanup

[JENKINS-20989] PeepholePermalink RunListenerImpl oncompleted should be triggered before downstream builds are triggered

This reverts commit fe1a1487.
It's been about a month, so I think it has served its purpose.

[JENKINS-26698] Localization follow-up