MINOR:code optimization in QuorumController (#13697)

1. add hint in switch item "BROKER_LOGGER" in ConfigResourceExistenceChecker, otherwise, it will be classified as default break and deleted directly. I don’t know if adding hint is better than deleting directly.
2. delete some unused variables and methods.
3. add the "@test" mark to a method in unit test that is forgotten.

Reviewers: dengziming <dengziming1993@gmail.com>

metadata/src/main/java/org/apache/kafka/controller/QuorumController.java

@@ -378,6 +378,7 @@ class ConfigResourceExistenceChecker implements Consumer<ConfigResource> {
         public void accept(ConfigResource configResource) {
             switch (configResource.type()) {
                 case BROKER_LOGGER:
+                    // BROKER_LOGGER are always allowed.
                     break;
                 case BROKER:
                     // Cluster configs are always allowed.
@@ -433,15 +434,6 @@ private NotControllerException newPreMigrationException() {
         }
     }
 
-    public static int exceptionToApparentController(NotControllerException e) {
-        if (e.getMessage().startsWith(ACTIVE_CONTROLLER_EXCEPTION_TEXT_PREFIX)) {
-            return Integer.parseInt(e.getMessage().substring(
-                ACTIVE_CONTROLLER_EXCEPTION_TEXT_PREFIX.length()));
-        } else {
-            return -1;
-        }
-    }
-
     private void handleEventEnd(String name, long startProcessingTimeNs) {
         long endProcessingTime = time.nanoseconds();
         long deltaNs = endProcessingTime - startProcessingTimeNs;
@@ -1586,11 +1578,6 @@ private void resetToEmptyState() {
      */
     private final FaultHandler fatalFaultHandler;
 
-    /**
-     * The slf4j log context, used to create new loggers.
-     */
-    private final LogContext logContext;
-
     /**
      * The slf4j logger.
      */
@@ -1823,7 +1810,6 @@ private QuorumController(
         boolean zkMigrationEnabled
     ) {
         this.fatalFaultHandler = fatalFaultHandler;
-        this.logContext = logContext;
         this.log = logContext.logger(QuorumController.class);
         this.nodeId = nodeId;
         this.clusterId = clusterId;

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

@@ -350,6 +350,7 @@ public void testFenceMultipleBrokers() throws Throwable {
         }
     }
 
+    @Test
     public void testBalancePartitionLeaders() throws Throwable {
         List<Integer> allBrokers = Arrays.asList(1, 2, 3);
         List<Integer> brokersToKeepUnfenced = Arrays.asList(1, 2);