include: make SDL_RenderPresent thread safety notes less verbose.

Reference Issue #7140.

include/SDL3/SDL_render.h

@@ -1393,10 +1393,7 @@ extern DECLSPEC int SDLCALL SDL_RenderReadPixels(SDL_Renderer *renderer,
  *
  * \param renderer the rendering context
  *
- * \threadsafety You may only call this function on the main thread. If this
- *               happens to work on a background thread on any given platform
- *               or backend, it's purely by luck and you should not rely on it
- *               to work next time.
+ * \threadsafety You may only call this function on the main thread.
  *
  * \since This function is available since SDL 3.0.0.
  *