command/partition: don't create null output in new partitions

No output at all is fine.  If the partition needs an output, it must
be moved there, but having just a null output isn't helpful.

src/command/PartitionCommands.cxx

@@ -105,8 +105,6 @@ handle_newpartition(Client &client, Request request, Response &response)
 					 AudioFormat::Undefined(),
 					 ReplayGainConfig());
 	auto &partition = instance.partitions.back();
-	partition.outputs.AddNullOutput(instance.io_thread.GetEventLoop(),
-					ReplayGainConfig());
 	partition.UpdateEffectiveReplayGainMode();
 
 	instance.EmitIdle(IDLE_PARTITION);