Core/VideoCommon: Fix duplicate OSD Custom Textures messages

Resolves duplicate OSD messages for Loading and Found custom textures.
VideoBackend initialization results in HiresTexture::Init being called.
We already call HiresTexture::Update when OnNewTitleLoad is called.
Thus we can remove HiresTextures::Init completely as it is redundant.

Source/Core/VideoCommon/HiresTextures.h

@@ -22,7 +22,6 @@ std::set<std::string> GetTextureDirectoriesWithGameId(const std::string& root_di
 class HiresTexture
 {
 public:
-  static void Init();
   static void Update();
   static void Clear();
   static void Shutdown();