GPUDevice: Improve texture pooling

src/util/metal_device.h

@@ -107,9 +107,6 @@ public:
 
   bool Create(id<MTLDevice> device, u32 width, u32 height, u32 layers, u32 levels, u32 samples, Type type,
               Format format, const void* initial_data = nullptr, u32 initial_data_stride = 0);
-  void Destroy();
-
-  bool IsValid() const override;
 
   bool Update(u32 x, u32 y, u32 width, u32 height, const void* data, u32 pitch, u32 layer = 0, u32 level = 0) override;
   bool Map(void** map, u32* map_stride, u32 x, u32 y, u32 width, u32 height, u32 layer = 0, u32 level = 0) override;