KAFKA-18845 Remove flaky tag on QuorumControllerTest#testUncleanShutdownBrokerElrEnabled (apache#19403)

It has been around two weeks since fixing
QuorumControllerTest#testUncleanShutdownBrokerElrEnabled PR
apache#19240 was merged. There is no flaky
result after 2025/03/21, so it has enough evidence to prove the flaky is
fixed. It's good to remove flaky tag.

Reviewers: Chia-Ping Tsai <[email protected]>

Author: FrankYang0529

metadata/src/test/java/org/apache/kafka/controller/QuorumControllerTest.java

@@ -374,7 +374,6 @@ public  void testElrEnabledByDefault() throws Throwable {
         }
     }
 
-    @Flaky("KAFKA-18845")
     @Test
     public void testUncleanShutdownBrokerElrEnabled() throws Throwable {
         List<Integer> allBrokers = List.of(1, 2, 3);