output/Filtered: eliminate FinishDestroy()

src/output/Control.cxx

@@ -377,7 +377,6 @@ AudioOutputControl::FinishDestroy() noexcept
 	if (thread.IsDefined())
 		thread.Join();
 
-	output->FinishDestroy();
 	delete output;
 	output = nullptr;
 }

src/output/Filtered.hxx

@@ -142,7 +142,6 @@ public:
 		   const ConfigBlock &block);
 
 	void BeginDestroy() noexcept;
-	void FinishDestroy() noexcept;
 
 	const char *GetName() const {
 		return name;

src/output/Finish.cxx

@@ -35,9 +35,3 @@ FilteredAudioOutput::BeginDestroy() noexcept
 	if (mixer != nullptr)
 		mixer_auto_close(mixer);
 }
-
-void
-FilteredAudioOutput::FinishDestroy() noexcept
-{
-	output.reset();
-}