Remove unused VoidChannelGroupFuture (#11376)

Motivation:

https://github.com/netty/netty/pull/11348 did remove the void promise API but did miss to remove the VoidChannelGroupFuture.

Modifications:

Remove class

Result:

Cleanup

transport/src/main/java/io/netty/channel/group/DefaultChannelGroup.java

@@ -49,7 +49,6 @@ public class DefaultChannelGroup extends AbstractSet<Channel> implements Channel
     private final ConcurrentMap<ChannelId, Channel> serverChannels = new ConcurrentHashMap<>();
     private final ConcurrentMap<ChannelId, Channel> nonServerChannels = new ConcurrentHashMap<>();
     private final ChannelFutureListener remover = future -> remove(future.channel());
-    private final VoidChannelGroupFuture voidFuture = new VoidChannelGroupFuture(this);
     private final boolean stayClosed;
     private volatile boolean closed;
 

transport/src/main/java/io/netty/channel/group/VoidChannelGroupFuture.java

@@ -1,181 +0,0 @@
-/*
- * Copyright 2016 The Netty Project
- *
- * The Netty Project licenses this file to you under the Apache License,
- * version 2.0 (the "License"); you may not use this file except in compliance
- * with the License. You may obtain a copy of the License at:
- *
- *   https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
- * License for the specific language governing permissions and limitations
- * under the License.
- */
-package io.netty.channel.group;
-
-import io.netty.channel.Channel;
-import io.netty.channel.ChannelFuture;
-import io.netty.util.concurrent.EventExecutor;
-import io.netty.util.concurrent.Future;
-import io.netty.util.concurrent.GenericFutureListener;
-
-import java.util.Collections;
-import java.util.Iterator;
-import java.util.concurrent.TimeUnit;
-
-// Suppress a warning about returning the same iterator since it always returns an empty iterator
-final class VoidChannelGroupFuture implements ChannelGroupFuture {  // lgtm[java/iterable-wraps-iterator]
-
-    private static final Iterator<ChannelFuture> EMPTY = Collections.<ChannelFuture>emptyList().iterator();
-    private final DefaultChannelGroup group;
-
-    VoidChannelGroupFuture(DefaultChannelGroup group) {
-        this.group = group;
-    }
-
-    @Override
-    public EventExecutor executor() {
-        return group.executor;
-    }
-
-    @Override
-    public ChannelGroup group() {
-        return group;
-    }
-
-    @Override
-    public ChannelFuture find(Channel channel) {
-        return null;
-    }
-
-    @Override
-    public boolean isSuccess() {
-        return false;
-    }
-
-    @Override
-    public ChannelGroupException cause() {
-        return null;
-    }
-
-    @Override
-    public boolean isPartialSuccess() {
-        return false;
-    }
-
-    @Override
-    public boolean isPartialFailure() {
-        return false;
-    }
-
-    @Override
-    public ChannelGroupFuture addListener(GenericFutureListener<? extends Future<? super Void>> listener) {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture addListeners(GenericFutureListener<? extends Future<? super Void>>... listeners) {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture removeListener(GenericFutureListener<? extends Future<? super Void>> listener) {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture removeListeners(GenericFutureListener<? extends Future<? super Void>>... listeners) {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture await() {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture awaitUninterruptibly() {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture syncUninterruptibly() {
-        throw reject();
-    }
-
-    @Override
-    public ChannelGroupFuture sync() {
-        throw reject();
-    }
-
-    @Override
-    public Iterator<ChannelFuture> iterator() {
-        return EMPTY;
-    }
-
-    @Override
-    public boolean isCancellable() {
-        return false;
-    }
-
-    @Override
-    public boolean await(long timeout, TimeUnit unit) {
-        throw reject();
-    }
-
-    @Override
-    public boolean await(long timeoutMillis) {
-        throw reject();
-    }
-
-    @Override
-    public boolean awaitUninterruptibly(long timeout, TimeUnit unit) {
-        throw reject();
-    }
-
-    @Override
-    public boolean awaitUninterruptibly(long timeoutMillis) {
-        throw reject();
-    }
-
-    @Override
-    public Void getNow() {
-        return null;
-    }
-
-    /**
-     * {@inheritDoc}
-     *
-     * @param mayInterruptIfRunning this value has no effect in this implementation.
-     */
-    @Override
-    public boolean cancel(boolean mayInterruptIfRunning) {
-        return false;
-    }
-
-    @Override
-    public boolean isCancelled() {
-        return false;
-    }
-
-    @Override
-    public boolean isDone() {
-        return false;
-    }
-
-    @Override
-    public Void get() {
-        throw reject();
-    }
-
-    @Override
-    public Void get(long timeout, TimeUnit unit)  {
-        throw reject();
-    }
-
-    private static RuntimeException reject() {
-        return new IllegalStateException("void future");
-    }
-}