Remove redundant thread sync counter draw_pending

The functions that used it already use a threadsafe FIFO queue
to communicate between threads and a sync to have the main thread
wait for the render thread.

Fixes #35718

servers/rendering/rendering_server_default.h

@@ -94,7 +94,6 @@ class RenderingServerDefault : public RenderingServer {
 	SafeFlag draw_thread_up;
 	bool create_thread;
 
-	SafeNumeric<uint64_t> draw_pending;
 	void _thread_draw(bool p_swap_buffers, double frame_step);
 	void _thread_flush();