[FLINK-18989][task] Remove non-sequental ChannelStateReader and the r…

…elated code

- ChannelStateReader and supporting classes
- methods for channel state recovery in inputChannels, subpartitions, etc.
- tests for reading channel state non-sequentially

flink-libraries/flink-state-processing-api/src/main/java/org/apache/flink/state/api/runtime/SavepointTaskStateManager.java

@@ -22,7 +22,7 @@
 import org.apache.flink.runtime.checkpoint.CheckpointMetrics;
 import org.apache.flink.runtime.checkpoint.PrioritizedOperatorSubtaskState;
 import org.apache.flink.runtime.checkpoint.TaskStateSnapshot;
-import org.apache.flink.runtime.checkpoint.channel.ChannelStateReader;
+import org.apache.flink.runtime.checkpoint.channel.SequentialChannelStateReader;
 import org.apache.flink.runtime.jobgraph.OperatorID;
 import org.apache.flink.runtime.state.LocalRecoveryConfig;
 import org.apache.flink.runtime.state.LocalRecoveryDirectoryProvider;
@@ -68,8 +68,8 @@ public LocalRecoveryConfig createLocalRecoveryConfig() {
 	}
 
 	@Override
-	public ChannelStateReader getChannelStateReader() {
-		return ChannelStateReader.NO_OP;
+	public SequentialChannelStateReader getSequentialChannelStateReader() {
+		return SequentialChannelStateReader.NO_OP;
 	}
 
 	@Override