Rewrite BrokerServiceTest#testBrokerStatsTopicLoadFailed

[lhotari]

The BrokerServiceTest#testBrokerStatsTopicLoadFailed is disabled by #20494.

2. Remove the test case and if the coverage is necessary, file a new ticket to add it back.

Originally posted by @tisonkun in #20494 (review)

The test BrokerServiceTest#testBrokerStatsTopicLoadFailed introduced in #19236 is invalid.

• It modifies the current shared state and that causes other tests to fail.
• The test uses Awaitility with a 2 minute timeout. That is too long for unit tests.

[github-actions]

The issue had no activity for 30 days, mark with Stale label.

[poorbarcode]

#22580 is trying to fix this issue