Revert "Fix T89204: slow repeated rendering with GPUOffscreen.draw_view3d"

This reverts commit d03b26edbd. There is some
refresh issue that needs to be solved before this can be enabled.

source/blender/python/gpu/gpu_py_offscreen.h

@@ -26,12 +26,8 @@ extern PyTypeObject BPyGPUOffScreen_Type;
 
 #define BPyGPUOffScreen_Check(v) (Py_TYPE(v) == &BPyGPUOffScreen_Type)
 
-struct GPUOffscreen;
-struct GPUViewport;
-
 typedef struct BPyGPUOffScreen {
   PyObject_HEAD struct GPUOffScreen *ofs;
-  struct GPUViewport *viewport;
 } BPyGPUOffScreen;
 
 PyObject *BPyGPUOffScreen_CreatePyObject(struct GPUOffScreen *ofs) ATTR_NONNULL(1);