Remove the AIO transport as NIO is just faster

The AIO transport was added in the past as we hoped it would have better latency as the NIO transport. But in reality this was never the case.
So there is no reason to use the AIO transport at all. It just put more burden on us as we need to also support it and fix bugs.
Because of this we dedicided to remove it for now. It will stay in the master_with_aio_transport branch so we can pick it up later again if it is ever needed.

testsuite/src/test/java/io/netty/testsuite/transport/socket/SocketTestPermutation.java

@@ -20,41 +20,28 @@
 import io.netty.bootstrap.ServerBootstrap;
 import io.netty.channel.Channel;
 import io.netty.channel.EventLoopGroup;
-import io.netty.channel.aio.AioEventLoopGroup;
 import io.netty.channel.nio.NioEventLoopGroup;
 import io.netty.channel.oio.OioEventLoopGroup;
 import io.netty.channel.socket.InternetProtocolFamily;
-import io.netty.channel.socket.aio.AioServerSocketChannel;
-import io.netty.channel.socket.aio.AioSocketChannel;
 import io.netty.channel.socket.nio.NioDatagramChannel;
 import io.netty.channel.socket.nio.NioServerSocketChannel;
 import io.netty.channel.socket.nio.NioSocketChannel;
 import io.netty.channel.socket.oio.OioDatagramChannel;
 import io.netty.channel.socket.oio.OioServerSocketChannel;
 import io.netty.channel.socket.oio.OioSocketChannel;
 import io.netty.util.concurrent.DefaultThreadFactory;
-import io.netty.util.internal.PlatformDependent;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map.Entry;
 
 final class SocketTestPermutation {
-
-    // TODO: AIO transport tests fail with 'An existing connection was forcibly closed by the remote host' on Windows.
-    //       Disabling test until the root cause is known.
-    private static final boolean TEST_AIO = !PlatformDependent.isWindows();
-
     private static final int BOSSES = 2;
     private static final int WORKERS = 3;
     private static final EventLoopGroup nioBossGroup =
             new NioEventLoopGroup(BOSSES, new DefaultThreadFactory("testsuite-nio-boss", true));
     private static final EventLoopGroup nioWorkerGroup =
             new NioEventLoopGroup(WORKERS, new DefaultThreadFactory("testsuite-nio-worker", true));
-    private static final EventLoopGroup aioBossGroup =
-            new AioEventLoopGroup(BOSSES, new DefaultThreadFactory("testsuite-aio-boss", true));
-    private static final EventLoopGroup aioWorkerGroup =
-            new AioEventLoopGroup(WORKERS, new DefaultThreadFactory("testsuite-aio-worker", true));
     private static final EventLoopGroup oioBossGroup =
             new OioEventLoopGroup(Integer.MAX_VALUE, new DefaultThreadFactory("testsuite-oio-boss", true));
     private static final EventLoopGroup oioWorkerGroup =
@@ -168,15 +155,6 @@ public ServerBootstrap newInstance() {
                                             .channel(NioServerSocketChannel.class);
             }
         });
-        if (TEST_AIO) {
-            list.add(new Factory<ServerBootstrap>() {
-                @Override
-                public ServerBootstrap newInstance() {
-                    return new ServerBootstrap().group(aioBossGroup, aioWorkerGroup)
-                                                .channel(AioServerSocketChannel.class);
-                }
-            });
-        }
         list.add(new Factory<ServerBootstrap>() {
             @Override
             public ServerBootstrap newInstance() {
@@ -196,14 +174,6 @@ public Bootstrap newInstance() {
                 return new Bootstrap().group(nioWorkerGroup).channel(NioSocketChannel.class);
             }
         });
-        if (TEST_AIO) {
-            list.add(new Factory<Bootstrap>() {
-                @Override
-                public Bootstrap newInstance() {
-                    return new Bootstrap().group(aioWorkerGroup).channel(AioSocketChannel.class);
-                }
-            });
-        }
         list.add(new Factory<Bootstrap>() {
             @Override
             public Bootstrap newInstance() {