[hotfix][tests] Remove dead code

flink-streaming-java/src/test/java/org/apache/flink/streaming/runtime/tasks/MultipleInputStreamTaskTest.java

@@ -29,7 +29,6 @@ import org.apache.flink.runtime.metrics.NoOpMetricRegistry;
 import org.apache.flink.runtime.metrics.groups.OperatorMetricGroup;
 import org.apache.flink.runtime.metrics.groups.TaskMetricGroup;
 import org.apache.flink.runtime.metrics.groups.UnregisteredMetricGroups;
-import org.apache.flink.streaming.api.functions.co.CoMapFunction;
 import org.apache.flink.streaming.api.operators.AbstractStreamOperatorFactory;
 import org.apache.flink.streaming.api.operators.AbstractStreamOperatorV2;
 import org.apache.flink.streaming.api.operators.Input;
@@ -415,21 +414,6 @@ public class MultipleInputStreamTaskTest {
 		}
 	}
 
-	private static class IdentityMap implements CoMapFunction<String, Integer, String> {
-		private static final long serialVersionUID = 1L;
-
-		@Override
-		public String map1(String value) {
-			return value;
-		}
-
-		@Override
-		public String map2(Integer value) {
-
-			return value.toString();
-		}
-	}
-
 	private static class TestBoundedMultipleInputOperatorFactory extends AbstractStreamOperatorFactory<String> {
 		@Override
 		public <T extends StreamOperator<String>> T createStreamOperator(StreamOperatorParameters<String> parameters) {