[hotfix][network] Cleanup the unused method from SingleInputGate

The method SingleInputGate#getConsumedResultId is never used, so remove it to cleanup the codes.

flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/SingleInputGate.java

@@ -254,10 +254,6 @@ public class SingleInputGate extends InputGate {
 		return numberOfInputChannels;
 	}
 
-	public IntermediateDataSetID getConsumedResultId() {
-		return consumedResultId;
-	}
-
 	/**
 	 * Returns the type of this input channel's consumed result partition.
 	 *