renderer/decoder: simplified audio PCM transcode

Turned the two-step PCM transcode into one step and simplified/removed much of
the unnecessary infrastructure that supported it. This makes the code cleaner
and generally improves the code paths.

app/core.cpp

@@ -48,7 +48,6 @@
 #include "project/projectimportmanager.h"
 #include "project/projectloadmanager.h"
 #include "project/projectsavemanager.h"
-#include "render/backend/indexmanager.h"
 #include "render/backend/opengl/opengltexturecache.h"
 #include "render/colormanager.h"
 #include "render/diskmanager.h"
@@ -119,15 +118,9 @@ bool Core::Start()
   // Set up node factory/library
   NodeFactory::Initialize();
 
-  // Set up the index manager for renderers
-  IndexManager::CreateInstance();
-
   // Set up color manager's default config
   ColorManager::SetUpDefaultConfig();
 
-  // Initialize disk service
-  DiskManager::CreateInstance();
-
   // Initialize task manager
   TaskManager::CreateInstance();
 
@@ -226,8 +219,6 @@ void Core::Stop()
 
   NodeFactory::Destroy();
 
-  IndexManager::DestroyInstance();
-
   delete main_window_;
 }
 
@@ -565,6 +556,9 @@ void Core::StartGUI(bool full_screen)
   // Initialize audio service
   AudioManager::CreateInstance();
 
+  // Initialize disk service
+  DiskManager::CreateInstance();
+
   // Initialize pixel service
   PixelFormat::CreateInstance();