Polish gh-6612 (#6932)

Signed-off-by: Johnny Lim <izeye@naver.com>

Author: izeye

micrometer-core/src/main/java/io/micrometer/core/instrument/binder/netty4/NettyMeters.java

@@ -192,6 +192,8 @@ public KeyName[] getKeyNames() {
 
     /**
      * Number of event executor workers.
+     *
+     * @since 1.6.0
      */
     EVENT_EXECUTOR_WORKERS {
         @Override
@@ -203,11 +205,6 @@ public String getName() {
         public Meter.Type getType() {
             return Meter.Type.GAUGE;
         }
-
-        @Override
-        public KeyName[] getKeyNames() {
-            return new KeyName[0];
-        }
     };
 
     enum AllocatorKeyNames implements KeyName {

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/netty4/NettyEventExecutorMetricsTests.java

@@ -128,7 +128,7 @@ void shouldCountWorkersForGenericIterableViaFallbackPath() {
         EventExecutor mockExecutor2 = mock(EventExecutor.class);
         Iterable<EventExecutor> genericIterable = Arrays.asList(mockExecutor1, mockExecutor2);
 
-        new NettyEventExecutorMetrics(genericIterable, Tags.empty()).bindTo(this.registry);
+        new NettyEventExecutorMetrics(genericIterable).bindTo(this.registry);
 
         assertThat(this.registry.get(EVENT_EXECUTOR_WORKERS.getName()).gauge().value()).isEqualTo(2.0);
     }