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);

src/output/MultipleOutputs.cxx

@@ -117,21 +117,6 @@ MultipleOutputs::Configure(EventLoop &event_loop,
 	}
 }
 
-void
-MultipleOutputs::AddNullOutput(EventLoop &event_loop,
-			       const ReplayGainConfig &replay_gain_config)
-{
-	const AudioOutputDefaults defaults;
-
-	ConfigBlock block;
-	block.AddBlockParam("type", "null");
-
-	outputs.emplace_back(LoadOutputControl(event_loop, replay_gain_config,
-					       mixer_listener,
-					       client, block, defaults,
-					       nullptr));
-}
-
 AudioOutputControl *
 MultipleOutputs::FindByName(const char *name) noexcept
 {

src/output/MultipleOutputs.hxx

@@ -78,9 +78,6 @@ public:
 		       const ConfigData &config,
 		       const ReplayGainConfig &replay_gain_config);
 
-	void AddNullOutput(EventLoop &event_loop,
-			   const ReplayGainConfig &replay_gain_config);
-
 	/**
 	 * Returns the total number of audio output devices, including
 	 * those which are disabled right now.