[FLINK-8250][runtime] Remove unused RecordSerializer#instantiateMetrics

This closes #5162.

flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/serialization/RecordSerializer.java

@@ -22,7 +22,6 @@ package org.apache.flink.runtime.io.network.api.serialization;
 import org.apache.flink.core.io.IOReadableWritable;
 import org.apache.flink.runtime.io.network.buffer.Buffer;
 import org.apache.flink.runtime.io.network.buffer.BufferBuilder;
-import org.apache.flink.runtime.metrics.groups.TaskIOMetricGroup;
 
 import java.io.IOException;
 
@@ -125,11 +124,4 @@ public interface RecordSerializer<T extends IOReadableWritable> {
 	 * @return <tt>true</tt> if some data is present
 	 */
 	boolean hasData();
-
-	/**
-	 * Instantiates all metrics.
-	 *
-	 * @param metrics metric group
-	 */
-	void instantiateMetrics(TaskIOMetricGroup metrics);
 }

flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/serialization/SpanningRecordSerializer.java

@@ -23,7 +23,6 @@ import org.apache.flink.core.memory.DataOutputSerializer;
 import org.apache.flink.core.memory.MemorySegment;
 import org.apache.flink.runtime.io.network.buffer.Buffer;
 import org.apache.flink.runtime.io.network.buffer.BufferBuilder;
-import org.apache.flink.runtime.metrics.groups.TaskIOMetricGroup;
 
 import javax.annotation.Nullable;
 
@@ -178,8 +177,4 @@ public class SpanningRecordSerializer<T extends IOReadableWritable> implements R
 		// either data in current target buffer or intermediate buffers
 		return (targetBuffer != null && !targetBuffer.isEmpty()) || lengthBuffer.hasRemaining() || dataBuffer.hasRemaining();
 	}
-
-	@Override
-	public void instantiateMetrics(TaskIOMetricGroup metrics) {
-	}
 }