WGL: Get rid of the use of the Host_GetRenderWindowSize() call.

Just use the Windows API to accomplish the same thing (this is what is done in Update()).

This makes the backing window handle the correct data-type for Windows for easier use in function calls.

Source/Core/DolphinWX/GLInterface/WGL.h

@@ -22,5 +22,5 @@ public:
 	void Update();
 	bool PeekMessages();
 
-	void* m_window_handle;
+	HWND m_window_handle;
 };