remove unused field. (#6747)

Co-authored-by: qiulu3 <Lucas209910>

shardingsphere-scaling/shardingsphere-scaling-core/src/main/java/org/apache/shardingsphere/scaling/core/execute/executor/channel/MemoryChannel.java

@@ -31,8 +31,6 @@ import java.util.concurrent.BlockingQueue;
  */
 public final class MemoryChannel implements Channel {
     
-    private static final int PUSH_TIMEOUT = ScalingContext.getInstance().getServerConfiguration().getPushTimeout();
-    
     private final BlockingQueue<Record> queue = new ArrayBlockingQueue<>(ScalingContext.getInstance().getServerConfiguration().getBlockQueueSize());
     
     private final AckCallback ackCallback;