cuda : disable unused cudaLaunchHostFunc code (#6078)

ggml-cuda.cu

@@ -11541,6 +11541,7 @@ static void ggml_backend_cuda_event_wait(ggml_backend_t backend, ggml_backend_ev
     if (ggml_backend_is_cuda(event->backend)) {
         CUDA_CHECK(cudaStreamWaitEvent(g_cudaStreams[cuda_ctx->device][0], (cudaEvent_t)event->context, 0));
     } else {
+#if 0
         // untested
         auto wait_fn = [](void * user_data) {
             ggml_backend_event_t event = (ggml_backend_event_t)user_data;
@@ -11548,6 +11549,8 @@ static void ggml_backend_cuda_event_wait(ggml_backend_t backend, ggml_backend_ev
         };
 
         CUDA_CHECK(cudaLaunchHostFunc(g_cudaStreams[cuda_ctx->device][0], wait_fn, event));
+#endif
+        GGML_ASSERT(false);
     }
 }