remove the set parallelism 1

remove the set parallelism 1

https://github.com/apache/incubator-wayang/blob/f8692b292d6e988f479699e6c5144fa5d4ba9bf2/wayang-platforms/wayang-flink/code/main/java/org/apache/wayang/flink/operators/FlinkObjectFileSink.java#L79

```java

assert inputs.length == this.getNumInputs();
assert outputs.length <= 1;
final FileChannel.Instance output;
final String targetPath;
if(outputs.length == 1) {
output = (FileChannel.Instance) outputs[0];
targetPath = output.addGivenOrTempPath(this.textFileUrl, flinkExecutor.getConfiguration());
}else{
targetPath = this.textFileUrl;
}

//TODO: remove the set parallelism 1
DataSetChannel.Instance input = (DataSetChannel.Instance) inputs[0];
final DataSink tDataSink = input.provideDataSet()
.write(new WayangFileOutputFormat(targetPath), targetPath, FileSystem.WriteMode.OVERWRITE)

```

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