Backport of benchmark broke build

Motivation:
2a2059d976 was backported from master, and included an overriden method which does not exist in 4.1.

Modifications:
- Remove the invoker method from NoPriorityByteDistributionBenchmark

Result:
No more build error

microbench/src/main/java/io/netty/microbench/http2/NoPriorityByteDistributionBenchmark.java

@@ -21,7 +21,6 @@ import io.netty.channel.ChannelConfig;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelHandlerInvoker;
 import io.netty.channel.ChannelMetadata;
 import io.netty.channel.ChannelOutboundBuffer;
 import io.netty.channel.ChannelPipeline;
@@ -298,11 +297,6 @@ public class NoPriorityByteDistributionBenchmark extends AbstractMicrobenchmark
             return channel.eventLoop();
         }
 
-        @Override
-        public ChannelHandlerInvoker invoker() {
-            throw new UnsupportedOperationException();
-        }
-
         @Override
         public String name() {
             throw new UnsupportedOperationException();