The current NetworkEnvironment would be the default ShuffleService implementation in task manager. In order to make the interface simple, we try to avoid more interactive with NetworkEnvironment.
NetworkEnvironment#unregisterTask is used for closing partition/gate and releasing partition from ResultPartitionManager. partition/gate close could be done in task which already maintains the arrays of them. Further we could release partition from ResultPartitionManager inside ResultPartition via introducing ResultPartition#close(Throwable). To do so, the NetworkEnvironment#unregisterTask could be totally replaced to remove.